I think the dev's probably more into M/M stuff to be honest. There's a lot, and I mean A LOT more stuff leaning that way, and M/M scenes seem to get more care than M/F ones. The female content might have been added more as a way to please people who aren't fans of M/M than to actually have a balance of content. But yeah, even if you're trying to play dominant, it's clear the aim is for the PC to be submissive...
The skew towards M/M doesn't come from the dev, but rather that new content is often voted on by the supporters, and they overwhelmingly want M/M content. So when most of the people actually paying him want M/M, then that's what he makes. If people want more M/F or F/F than they're already getting, then they should pay the creator.
Personally I speculate the straight people are so used to being catered to that they have become "spoiled" and don't want to pay, while gay folk are happier to sink money into something that is actually for them. I'm obviously just guessing as to why, but when a demographic that represents less than 10% of potential customers have a bigger representation then there's obviously
some reason.
But the fact remains that the paying customers prefer M/M, so that's what they get. Personally I'd like more M/F, but I'm not paying him, so can't really fault the guy for not putting my desires above the people paying his bills.