Maaaaaaybe because most games are focused on combat and mechanics and In that context, It's hard to explore if they like dick or vag. I mean, Samus and Chell might just as well be asexual 5,7 ft tall cubes of Tofu for all that their clitoris matter to the plot. The same could be said about Doom Guy's and Adol the Red's prostates. Two examples were brought up in this thread which exemplify what I am talking about, Overwatch and TaleTell's Walking Dead. In Overwatch every non white, non straight character feels like pandering when those aspects are brought up because that doesn't matter in an online shooter, when in TWD which is a game about humans and the decisions that they make in a given time and place, you need to know who they are and stuff like race, gender and sexual preference become relevant because It's actual writting and not pandering.
This.
It brings up an interesting point: who's sexualizing who? Who other than SJWs and troons are so hellbent on characters' genitals being the focal point of the whole goddamned game? Most players are preoccupied with shooting shit, discovering secrets and unlocking achievements. They don't have time to stop and think "You know Samus has a vagina and there is some deeper meaning behind that." More like, "That's the fastest I've ever gotten 'Sky Missile.'"