The Google Books optical character recognition tool does a poor job of reading books printed in blackletter, which was the dominant form of English printing until the late 1500s—so Google Books is not very good at finding instances of particular words from texts of the blackletter era.
Nevertheless, in one instance Google Books was able to find a match for Satan because it appears in roman type because Satan is the a character in a play. From the opening scene of Thomas Lupton, A Moral and Pitieful Comedie, Intituled, All for Money: Plainly Representing the Manners of Men and Fashion of the World Nowe-a-days (1578):
Here commeth in Satan the great deuill as deformedly dressed as may be.
Satan. Ohe, ohe, ohe, ohe, my friende Sinne I was neuer so merrie
In hearing thy qualities I cannot be wearie:
Slightly earlier instances appear in Thomas Owen, Godly Contemplations for the Unlearned (1575) [combined snippets]:
Sathan the author a father of all lyers & slanderers. And hereby we may easily come to find the first offspring of all these calumnies : the first & only author and teacher of all calumniators, is Satan the head calumniator himselfe. Who knoweth not this ancient fraud & accustomed fetch of that comon enemy both of God & all mankind who hath no more potent meanes to resist the honour of God, to oppresse his seruants, and hinder the progress of true vertue and ...
in John Collier, The Rocke of Regard, Divided into Foure Parts (1576):
Attending still, when triall of my fayth
Shall treade downe death, and Sathan force to reele,
And boldly fay, till latter gaspe of breath,
My soul through faith the joyes of heaven doth feele.
and in Innocent Gentillet, A Discourse upon the Meanes of Wel Governing and Maintaining in Good Peace, A Koingdome, or Other Principalitie (1577/1602):
Fo whe[n] the cleare light of the Gospell began first to spring and appeare, Sathan (to occupie and busie mens minds with toyish playes and trifles, that they might give no attendance unto true wisdome) devised this policie, to raise up jeasters and fooles in Courts, which creeping in by quipping and prettie conceits, first in words and after by bookes, uttering their pleasant ieasts in the Courts and banquets of kings and princes, laboured to root up all all the true principles of Religion and Policie. ...
For than Sathan being a disguised person amongst the French, in the likenesse of a merrie jeaster, acted a Comædie, but shortly ensued a woeful Tragœdie. ... Moreover Sathan useth strangers of France, as his fittest instruments to infect us stil with this deadly poyson sent out of Italie, who have so highly promoted their Machivelliam bookes, that he is of no reputation in the Copurt of France which hath not Machiavels writings at the fingers ends, and that both in the Italian and French tongues, & can apply his precepts to all purposes, as the Oracles of Apollo.
And similarly, from Geffrey Whitney, The Choice of Emblemes (1586, page 129):
And as the surge doth worke both daie, and nighte,
And shakes the shore, and ragged rockes doth rente:
So Sathan stirres, with all his maine, and mighte,
Continuall siege, our soules to circumuente.
From George Gifford, A Dialogue Concerning Withes and Witchcraft (1593):
Daniel. ... And in the Reuelation chapter 12. all the deuils make that great red dragon: And out Saviour doth shewe how close they ioyne in one, when he saith, If Satan be deuided against Satan, or if Satan cast foorth Satan, how shall his kingdom endure? Matth. 12. now then, whether the witch deale, as she supposeth, with one spirit, or with manie, it commeth all to one effect, thus farre, that one dealeth not alone, but with the helpe of others. So that he or she that hath familiaritie with one deuill, it is as much as if it wer with an hundreth. Moreover, the deuils be spirits, they have no bodily shape or likenesse but yet can make an appearance of a shape, as appeareth by the inchanters before Pharao, when their rods were turned into serpents in shew. Exod. 7. And then one deuill can seem to be foure or five, and foure or five can seeme to be one: It is therefore but the craft of Satan, to make shew of more or lesse.
M. B. [Schoolmaster.] Do you not thinke then, that where the more deuils be, there is the greater power of Satan?
From Robert Roche, Eustathia, Or the Constancie of Susanna (1599):
For as he faithful Abrahams heart, did proue,
By willing offring, of his guiltlesse sonne;
And tride Iobs stable faith, and constant loue,
What time she Sathan, his consent had wonne,
To leaue Iobs health forlorne, and wealth vndone:
Even so he sifted, Susans constancie,
If that shee would, her pure faith falsifie.
And to complot this treason, by temptation,
False Sathan had fit men, fit time, fit place;
Was never foe so fitted for invasion,
The plot once laid he would not bate an ace,
The price was shame (her glories dim disgrace)
The meanes, the men, the time, the place, thus fitted;
Yet Sathan prov'd a foole, and shallow witted.
From "W.S.," The Puritaine: or, The Widdow of Watling Street (1607):
Widow Plus. Tempt me not Satan.
Sir Godfrey. Satan? Do I looke like Satan? I hope the Deuill's not so old as I, I tro.
And from Johannes Boemus, The Manners Lawes and Customes of All Nations (translated 1611):
Had not Satan the Prince of the world, and enemie of mankind, (by sowing his most pestilent Cockles among the good corne) confounded their most intire and happie estate. ...
Moreover also, after Christ Iesus, ... had confounded their damnable idolatry and spread abroad a new religion, and new institutions of life, yea and preuailed so much, as being receiued of all nations in the world, there could nothing more be desired for the obtayning of true felicity: when Satan returning into his former malice,and going about to circumuent,and get againe his habitation in mens curious hearts,which before (by the comming of Christ) hee was forced to forsake, reduced some into their former errors, and so corrupted and blinded others with new hereticall opinions, as it had been better for them, neuer to haue tasted the truth, then so sodainely and maliciously to forsake the knowne way of saluation.
In addition to all of these instances, we have The Bible. Translated according to the Ebrew and Greeke, and conferred with the best translations in diuers languages (1605), which, according to Google Books, contains 49 pages with one or more matches for Satan, but in fact has many more, since once again Google Books' OCR struggles to pull the word Satan out of the blackletter text of the Bible itself, but does better finding the word in the roman accompanying notes. Particularly noteworthy is the Book of Job, in which Satan makes a memorable entrance in verse 6 of chapter 1:
6 Now on a day, when the children of God came and stoode before the Lord, Satan came also among them.
7 Then the Lord sayde unto Satan, Whence commest thou? And Satan answered the Lord, saying, From compassing the earth to and fro, and from walking in it.
Conclusions
The foregoing examples present Satan (or Sathan) as a familiar figure to readers of the the period 1575–1611. And I see no reason to suppose that this familiarity arose suddenly in 1575.
The problem with searches of earlier books is that they run afoul of the books' hard-to-read blackletter type. But for evidence that Satan is not a latecomer to popular discourse in English, consider that he receives three mentions in the Man of Law's Tale in The Canterbury Tales (1387):
O Sathan enuious / syn thilke day
That thou were chaced from outr heritage
Wel knowestow / to wommen the olde way
Thou madest Eua / brynge vs in seruage
Thou wolt fordoon / this cristen mariage
...
Sathan / that euere vs waiteth to bigile
Saugh of Custance / al hire perfeccioun
And caste anon / how he myghte quite hir while
And made a yong knyght / þat dwelte in that toun
Loue hire so hoote of foul affeccioun
...
Allas Custance / thou hast no champion
No fighte kanstow noght so weylaway
But he / that starf for our redempcion
And boond Sathan / and yet lith ther he lay
So be / thy stronge champion this day
Likewise, Sattan plays a prominent role in "The Harrowing of Hell" in the York Mystery Plays (14th to 16th centuries):
Belsabub. What þanne, is lymbus lorne, allas!
Garre Satan, helpe þat we were wroken,
Þis werke is worse þanne euere it was.
Sattan. I badde ʒe schulde be boun
If he made maistries more,
Do dynge þat dastard doune,
And sette hym sadde and sore.
So it may be that English speakers have been on more or less intimate terms with Satan/Sathan/Sattan since before Middle English gave way to Modern English. In a culture steeped in Christianity, familiarity with the Bible's various human, angelic, and diabolical characters must have been very widespread indeed. And Satan is certainly one of the more visible malevolent figures in it. I would be very surprised if demonic characters such as Satan, Lucifer, and Beelzebub were not as well known in their way as heroic figures such as Samson, Judith, and Joshua were in theirs.
Best Answer
I don't think it has to do with them being verbs, and for the most part, I also don't think it has to do with the etymology. I think it mainly has to do with the stress patterns of these words.
The tendency I see is that the letter L is generally doubled after a stressed short vowel, and not doubled after an unstressed vowel. Historically, there has been a lot of variation in the spelling of words like this. Based on etymologies that I have looked up, I would say there is little to no etymological significance to the use of a single L vs. a double L at the ends of words. It's just an oddity of our modern spelling system. (Another relevant question about double L: Why is there a double "ll" in "bell"?)
Here are some actual examples: mill (as you've found out, it comes from Old English mylen), small (comes from Old English smæl), skill (comes from Middle English skele, scele, skile, skyle, from Old Norse skil), dill (from Old English dili, dile, dyle). On the other hand, metal comes from Latin metallum with a double L (although the French spelling metal may have also played a role, as French seems to have been an intermediary in the transmission of this word). I have some more examples of words like metal in my answer here: Adding an L when appending an -ium suffix to a word? (Metallium vs. Metalium)
Monosyllabic content words always end in a stressed syllable, and polysyllabic verbs are more likely than nouns to end in a stressed syllable. These two factors are probably why it seemed to you that this was related to part of speech.
There are many nouns that end in "-ill," especially monosyllables such as bill, hill, sill, and frill. Adjectives such as still can also have this spelling.
There are also verbs that end in "-il." Aside from bedevil, there are cavil, imperil, stencil, fulfil (British spelling; Americans use fulfill). However, it does seem to be true that fewer verbs than nouns end in "-il."
What is the etymology of words that end in -il?
It's worth noting that there aren't that a huge amount of words in total that end in -(consonant)-il."
As you've found, many of them are derived from Latin nouns ending in -illus, -illa or -illum. When Latin nouns are taken into English, final -us, -a and -um are often simply removed, which explains how we get English nouns ending -ill or -il.
Latin verbs, however, are usually borrowed in a more complicated fashion. For complicated historical reasons, Latinate verbs in English are generally derived from the past participle form of the Latin verb. Latin past participles generally have a dental suffix (usually t) that is retained in the derived English verb. So for example, the Latin verb inficio corresponds to the English verb infect. In regular verbs of the first declension (the most common type) this dental suffix is preceded by the vowel a. So Latin verbs containing -ill- have generally been borrowed as English verbs ending in -illate. (For example, scintillate comes from Latin scintillare). That might be a contributing factor to the relative rarity of verbs ending in "-il."
There are various other sources for words ending with "-il." In most cases, the modern spelling with "il" is fairly straightforward based on the etymology.
However, there are a handful of words that seem to have acquired the spelling "-il" for unclear reasons. Here's what I mean: devil (Old English deofol), evil (from Old English yfel), weevil (Old English wifel), stencil (earlier spelled stancel; interestingly, the Oxford English dictionary says that the noun is derived from the verb). I don't know how to explain these.