I mean, the same can be said for blackmail. My assumption has always been that it's one of the most prevalent tropes on this site here, it at least seems to pop up very often to me.
Quite true, but the blackmail scenario allows for a wide range of potential character conflicts, which is why it is so popular for game designers and book authors alike.
As for dramatic tension I don't necessarily see that as an issue to apply without blackmail, you just have to have the writing chops for it. Besides, even without "dramatic tension" I could still enjoy the sexual fantasy alone were it there.
And, indeed, there are such games. But they are few, and generally much less-well-supported than the blackmail games.
She could also just do it because she gets off on it. Women can be perverts.
The only reason why I didn't when I was her age was because it would have meant social castration in the community that I grew up in and my family lived in. Those constraints are not on this MC, you could easily use the condition from her witness protection program for her to let loose. What better way to hide your old self than leave the prudish girl behind and explore your sexual limits?
I'd dig that personally.
Again, there are games like this. But of there is no inner conflict for the character, they tend to be less popular (I, for one, find the biggest one of those, Tamara's Exposure, terminally boring).
Making it a mission wouldn't necessarily have to be a requirment, just make a route where the sexual themes themselves are the point like I mentioned. For example she could get involved with a daring girl group who challenge each other to ever-increasing sexual dares for the hell of it.
MC's old life is practically over, there's no limits to what kind of things you could really get her in to now that she has the opportunity to re-invent herself.
You are describing
Naughty Lyanna to a T. But that game's already been made, and made extremely well. What's the point of remaking it with less graphical skills?
I understand where you are coming from, and have enjoyed some of the games made along the lines you propose, but I can also understand why a new game developer would want to use a more familiar trope that has proven at least as popular.