I suspect because the phrase was only needed for women and widower is a much later literary invention.
Widow had a lot of legal implications for property, titles and so on. If the survivor of a marriage was a woman things got complicated before women had many rights.
If the survivor was a man in the middle ages it didn't really make much difference as he held all the property anyway.
A similar question came up about illegitimate girl children, there was no word because there was no legal need to consider them.
For the rest - English generally doesn't have many genders anymore and those that have survived are where it was necessary to know the actual sex. So for example "actress" once had rather more of a euphemism role (like the modern 'model actress whatever') — where knowing their sex is relatively important.
The definition of a fishwife is tied to both of the definitions you listed. Wikipedia's article on the fishwife explains that:
A fishwife or fish fag is a woman who sells fish.... Fish women were notoriously loud and foul-mouthed as in the expression, To swear like a fishwife. One reason for their outspokenness is that their wares were highly perishable and so lost value if not sold quickly.
Unlike its common usage today, wife meant any woman, not just a married one. Some words still retain this meaning:
This usage stems from Old English wif (woman) and is akin to the German weib, also meaning "woman". This sense of the word is still used in Modern English in constructions such as midwife and old wives' tale.
So historically, a fishwife was just a woman who sold fish. Over time, since fishwives were often "loud and foul-mouthed," their job title became synonymous with your definition of "a bad-tempered woman with a loud voice."
Interestingly, fishwives have had different reputations in different areas. In Billingsgate, there were "the wives of Billingsgate" who:
dressed in strong 'stuff' gowns and quilted petticoats; their hair, caps and bonnets were flattened into one indistinguishable mass upon their heads. ... They smoked small pipes of tobacco, took snuff, drank gin and were known for their colourful language.
On the other hand, the fishwives of Newhaven, Scotland were:
noted for their beauty and industry, and celebrated by royalty.
Best Answer
tl;dr: So long as you are content with historical terms rather than merely contemporary ones, the precise word you are looking for is coquet.
Here’s why.
The OED says that a coquette is first:
Curiously, it also provides a later subsense:
Where we learn that the sense B 1 of coquet is
Whence we learn of this curious etymology:
The pronunciations given for both are identical.