yeah, there genuinely is multiple problems with asking that. You make it sound like the devs can just snap their fingers and with minimal effort implement that. Since i'm guessing you aren't asking for a straight model replace, replacing the male character with a female with a strap-on, they will have to redo every scene from scratch. You are actually asking them to double the amount of content they are putting into the game. Content that isn't going to appeal to most of their original supporters.
So by that logic it's okay for me to go into all straight games and request they take months out of development to implement complete gay coverage, and therefore requiring them to half the rate they put out future content to support it when they finally catch up? And the devs are doubling the amount of content, they are going to increase the price. You want to pay 50% more for something when you are only interested in half of the game?
Not every game is going to appeal to everyone. If, when the game is complete, you want to request they work on and release a separate straight version, go right ahead. Depending on interest that might be a good move financially. But i guarantee you shifting gears in the middle of a project is a surefire way to hemorrhage subscribers now and including it all in one package with an increased price is just going to make less people buy it on release.