As someone who's worked on actual TL work in the past, I can tell you anything that is done in MTL will usually never get an actual translation as there's not as much market for them anymore. MTLs are killing the practice of actual translation work.
99% of those games will never see "proper" translation anyway, and at least 95% of them is shovelware anyway and everyone know it. And with AI-art generators it will become even more true than even with stock 3DCG goblinas.
Another thing is that even official translations are often rewrites that only partially have something to do with original, so it's even worse than pure MTL anyway because so-called "translators" are basically use someone else's game to insert their own fanfics, or else they don't know what are they translating and just insert whatever shit they can come up with, or editor rewrites dialogues to "adapt" to his own tastes, current year agenda, and things like that.
Sure, MTL can be bad if done by idiots who don't understand how to use those tools, of if they use totally outdated models/services/programs, or if they never edit the result even a little, or if there's text that you won't understand outside of game context, and it can sprout gibberish or unrelated text, but it's hardly worse than translators who barely/palatially understand Japanese (and maybe even English too), or who insert their own ego where it doesn't belong, or work at snail pace because of this or that reason.
People who can actually translate from Japanese on high level either don't work with games at all, much less hentai games, or doing it on a whim in their free time. And there's only so much of them, so they only work with handful of games. You lament that MTLed games won't get translation, but that's hardly the case - popular games are getting proper translations regardless, and the rest of them wouldn't be translated without MTL either way. Maybe like 0.5% of them and years later, if you're lucky.
Most Japanese VN devs probably think it's not worth the extra costs.
Most of the time it's true, and even Steam release wouldn't bring much on their table to be worth it, or even drive them bankrupt if sales are bad. It's basically a gamble - you spend buttload not only on game itself, but on translation on top of that, but might never see the return of investment. Hardly anyone want to risk like this. MTLs, on the other hand, cost nothing, and can produce passable result. Especially, again, if devs aren't idiots and at lest edit and test the results. Most people are content with shovelware having passable translation - just enough to understand where to go, what to do, and overall story outline. VN's are one thing, but actions, puzzles and even RPG's can get away with it.