You must be able to talk.
Wands function by using the Spell Trigger method of item activitation. And Spell Trigger says in its description:
Spell trigger activation is similar to spell completion, but it’s even simpler. No gestures or spell finishing is needed, just a special knowledge of spellcasting that an appropriate character would know, and a single word that must be spoken. Anyone with a spell on his or her spell list knows how to use a spell trigger item that stores that spell. (This is the case even for a character who can’t actually cast spells, such as a 3rd-level paladin.) The user must still determine what spell is stored in the item before she can activate it. Activating a spell trigger item is a standard action and does not provoke attacks of opportunity.
If you can't talk, you're not going to be able to speak that single word, so you won't be able to activate the Wand.
You do not generally use wands or wondrous items for offense. The artificer class from Eberron Campaign Setting can make it work, but for pretty much everyone else it just costs too much no matter how you do it. Wands and wondrous items that use spells are usually used for utility, stuff you can do out of combat.
The reason why is because in combat, the most precious things in the game are actions. The vast majority of combats are decided in the first 2-3 rounds—many in the very first. You only have so many opportunities to do something to change the outcome of the fight. That means that your actions in combat have to be very, very potent. Spells can often do that—but they need to be reliable. That means high saving throw DCs, that means high caster levels, and so on, and magic items do not offer these.
In contrast, out of combat, you can take more time. If something only has caster level 1st and so only lasts one round: no problem, you can take the time to just keep using it. If something has a save DC of 11 because that’s the minimum for a 1st-level spell and magic items use the minimum possible value, that’s fine because it’s not an attack, it’s healing an ally or lighting a hallway or whatever.
So basically, your concern is rather moot: the real answer is that neither of these things is used for the purposes you’re imagining.
This does lead us to the more direct answer to your question: 50 charges is more-than-enough for a whole lot of spells. If you find a wand of magic missile with caster level 1st, you simply don’t care that it’s only got 50 charges: you are going to reach a point where caster level 1st magic missile is just not worth using at all because your actions are too precious. Might as well see the savings up front. After all, command-word items cost more than double what a wand does. That’s a really big deal.
TL;DR: Command word items cost double what the comparable wand does, and for most spells, 50 charges is more than enough as it is. Many spells just aren’t useful when cast from items, and that includes almost all you would attempt to use offensively.
Best Answer
For the purposes of this answer, I am assuming that the DM is running everything just as given in the book, even when they are just recommendations or suggestions and the rules explicitly acknowledge the possibility of exceptions.
The rules don’t really entitle you to anything
You are affirming the consequent, unfortunately. The rules state that if an item costs more than the town’s limit, you definitely won’t find it. The converse, that if it does not cost more, you definitely will find it, is not necessarily true.
I personally think they should...
Now, generally speaking, I think this is a problem and that the rules more-or-less should also guarantee that items within such limits are available. Many classes are utterly dependent on magic items, and not just on the general concept, but on getting certain specific magic items, to function on anything like a level-appropriate level. Failure to get them results in a character significantly less powerful than his or her level would otherwise indicate, and the exact degree to which his or her power has been reduced is rather difficult to judge. (Of course, this would matter a lot more if CR was at all reliable to begin with, which of course it is not; encounters were judgment calls anyway. But exacerbating that unreliability by moving away from the assumptions baked into the system only makes such judgment calls harder.)
...but would make partially-charged wands an exception to that anyway
But in the case of partially-charged wands, those are particularly problematic. A 1-charge wand costs 60% what a scroll of the same spell at the same caster level costs, but is more durable, more easily kept accessible, and easier to use (both for spellcasters and those making Use Magic Device checks). There is therefore absolutely no reason to ever have a scroll if you could get a 1-charge wand instead.
Furthermore, you cannot make partially-charged wands: new wands always have 50 charges. They only become partially-charged through using up charges. Therefore, no one can make a business crafting and selling partially-charged wands: the only place you could hope to find them is in a pawn shop. This gives a rather significant reason why you should not expect them to be regularly available.