1. It's strange to control a female character to have sex when you're male, and often times the protangonist may end up with being turned to a lessibian.
2. For the reason why female protangnoist ends up as a lessibian is that, if not, you can only focus on only one female involved in sex from that point of view while male players want to see more female characters in game.
What do you think?
It's strange
for some people to control a female character to have sex when they are male, but not all, not even a minority, quite a significant number have no problem, you just have to look at the number of games and their popularity. Unless you believe all those players are female.
While most female protagonist games seem to have at least a few lesbian scenes, most of the content generally is hetero, pure lesbian games seem a minority, so it's disingenuous to say players end up going lesbian route when most of the content is not focused on that, why do you think they would even make that if no one plays it. Most female protagonist games (majority of japanese rpg ones seem to be from what is presented here) focus on corruption, rape, humiliation, degradation, mind break etc, do you think that's made for a female audience.
In the OP you asked what are demerits of developing a female protagonist, to that end what you propose is not really a demerit, it's just personal preference. People who don't like NTR don't play games with NTR, same with Futa, vore, scat, etc. You have to know your audience going in, FPS games are probably the most popular type of video games (ignoring mobile games), that doesn't mean that strategy games have demerit because there's no first person perspective.
If you are actually thinking of developing a game, only go for themes and fetishes that interest you, most developers seem to do just that, don't force yourself to go for things that don't interest you. If you really want to challenge yourself and go for it, and having sex with other men revolts you then go for Vanilla lesbian games, no problem with that.
As for an actual demerit, I don't think there are any inherent ones but some games may require more effort in the writing department to make a female protagonist work. Also, I think female protagonists require more work in general compared to their male counterparts as the Female MC generally carries the game, while you can get away with a blank slate self insert protagonist with minimal personality in Male MC games if the rest of the game is decent. (just my opinion, haven't made a game or anything).
