Imagining a different sexuality is probably the same.

There are completionists out there who want to get every bit of possible story or every affordable achievement possible out of a game.

If written well (and that in itself is a challenge), I can see a game encouraging people to do a second playthrough as a different gender or sexuality just to unlock more of character backstories or achievements or whatnot. If that means some of them better understand what life is like for people of different genders or sexualities or learn something about themselves, that can only be a good thing.

It'd be a monumental task to develop such a game though. You'd need a writing team that fully understands all of this and a large enough cast where there are enough options for everyone. You can't just have one token character of each representation -- there still needs to be meaningful choices and characters that are deep enough where you can get invested in their story.

Having romanceable characters be "playersexual" drastically reduces the required size of the cast and all of the development benefits that come along with that. But by doing so, you aren't really representing diversity -- you're just making character identities mirror whatever the player wants them to be. This appeases LGBTQ+ players who want to be able to romance whomever they are attracted to but doesn't help with visibility to or acceptance from cis/het people.