or, rarely, she's simply bi or lesbian and maybe also a pervert with an incest fetish seducing her son or brother like a bunch I've come across. Kinda like the male MC but simply with genders reversed, but there's just a very limited number of plausible possible scenarios that actually require the MC to be female when you think about it.
Well, "plausible possible scenarios that actually require the MC to be female" is perhaps not the correct point of view, seeing how 50% of the world's population happens to be female.
So it's not the issue to requiring anything, it's sometimes just interesting to see things from a female POV, even if you are a male.
Also, not sure what's wrong with female protagonists who are "simply bi or lesbian and maybe also a pervert with an incest fetish seducing her son or brother
".
I happen to like such games.
But in general, I tend to self-insert (up to a point), so games where I play as a male MC, I am not that much interested into fucking anything that moves but more into fucking girls which interest me, either because of the incest / body type, or, in the rare case of well written games, the girl's personality.
In games where I play as a female MC, I imagine the MC to be my sister, daughter or mother (depending on the scenario) and make choices that I would like them to make, or which I would find hot. Which tends to mean that they are more likely to start a lesbian relationship with their sister rather than to jump on the first BBC they come across.
So I fully agree with your dislike for mindless corruption games, also fully agreed regarding your thoughts about "Not a world for Alyssa", but that doesn't mean that every FMC game has to be like that.