This is a pet-peeve of me as well. Putting the content the player actually wants to see behind lose-conditions is just bad game design. You are supposed to reward the player for playing well. Not for intentionally failing at the game.
I think this trope is so prevalent because many game designers think in stock game genres that are simulations of conflict resolutions through violence: JRPGs, action-adventures, fighting games, shoot-em-ups, platformers... these are all genres where you usually kill or be killed. When you then try to add sex to these game mechanics, then there are really just three possible ways to do that:
- Sex when the player defeats an enemy, which essentially turns the player into a rapist. Sure, some people are going to enjoy this. And I would have to lie if I said that I never enjoyed a game with non-consensual sex. I am a dominant and a sadist, so the fantasy does appeal to me. But it just feels wrong to me to create such a game, because it stands in dissonance with my own personal moral value that BDSM without consent is abuse.
- Sex when the player is defeated. This doesn't have that unfortunate connotation, and allows the player to experience rape fantasies without feeling the guilt of being the assailant. But it rewards the player for losing which is, as I mentioned before, just bad game design.
- Sex shown separated from the game mechanics, for example in cutscenes between levels. Which leads to the porn feeling disconnected from the gameplay and shoehorned in.
So what's the solution?
We need to stop thinking in traditional genre conventions and figure out more original ways to gamify sexuality.
[begin shameless self promotion] In my submission to this jam, Tentaculord, I went for the tentacle sex trope; a mainstay of hentai and almost always framed as non-consensual. But with the twist of having a "victim" who explicitly and enthusiastically consents to being dominated and violated. Consensual non-consent can be a good way to frame an adversarial game mechanic in a non-rapey way. In my game before, Fling League, I framed it all as a sports competition with consenting participants. This "game within a game" framing can also be a good way to make an inherently violent game mechanic seem less violent. [end shameless self promotion]