Honestly, there's an issue here I don't think you give remotely enough credit to.
While I do personally agree that it's good to see supporting female characters, in a medium as visual as VNs this problem is something devs often have to legitimately deliberate.
Most people don't really care if every character in a game aimed primarily at gay men is male. However, there's a very annoying and vocal contingent of people that will bitch to no end if a female appears, even as a supporting character. The inverse happens to straight games, too.
So when it's a deliberate choice, it's often less about providing fan service, and more about just... avoiding issues related to adding females. There's the aforementioned group, but also the group that'll complain if the females are too simple, or too stereotypical, etc etc.
I get your point, mind you, but I think it's worth looking at the other side of things, too.