I kind of understand your point. I thought about something a while ago and realized that while by number i mostly play games with male MCs, my top favorites have female MCs in them. The explanation is quite simple: i don't really associate myself with the MC when i play, even if i rename or customize them, and in games where the protagonist is a guy there are usually only 1-2 women i find interesting or fun and the rest of them tend to become fillers, while if i don't like a female MC i drop the game fast, but if i like her, then i'm guaranteed to have a girl i like through the whole story.
That being said, i think the key to your opening question is in the term "corruption". Finding such a powerful satisfaction in hedonism that one would give up everything else for it is a powerful fantasy. In these games i think that's the goal and so the full corrupted, full lust ending is the true one, while the pure and happy end is only there to emphasize the power of pleasure by showing what the MC gave up for it.
In this sense you are not punished for picking the sex filled route, rather the pure one is only there for set dressing.
Personally i prefer a lighter approach where these games and stories are in a "hentai universe" with it's own set of logic. One of my favorites, the game that brought me to this forum is a fantasy game with female MC and technically corruption mechanics as she becomes more accepting to more taboo things as her lust stat grows. But while she starts the game with the only goal of dying to get revenge, over the story and through this "corruption", she finds not only lust, but acceptance, friendship and love in most endings.
So yeah, even tho i checked out a good amount of genres here out of curiosity, i found out that i'm also not looking for misery.