i'm not a fan of this kind of design either (i once played such a game and could not figure out where the sex scenes were because it was fairly short and i just happened to never die!!), but i don't know that it's deliberately sex-negative. i think it might just fall out naturally for the wrong reasons —
- most such games seem to be platformers, where the player is constantly in motion, and stopping them (sex is a very in-place activity) is kind of antithesis to the mood of the game, but the only natural stopping point is defeat
- sex does often come with a climactic moment at which point you are done with the sex, so, there's a rather strong parallel there
- "what if a thing i like were done to me" is a very common background radiation kink
- and of course a lot of other games do it so it becomes just a thing to do
i don't really know what the solution is though, other than to simply develop a lot of kinks and base the game around those instead
or just go super cartoon with it and have penetrative-sex-based mechanics. land on stuff with your butt and use that to jump higher idk