I think it's a lot about how a girl presents herself. If you go around showing off "what you got", obviously you will build an audience faster, but it's a perverted audience. You could also just be born attractive as hell so people are gonna want to watch you more easily. I'm not one hell of an attractive girl nor do I do that showing off thing and I'm building my audience very slowly. I want a true audience so that's why I'm not doing any of those things, plus I'm just a 15 year old girl, should have some sense in my head.
Also, if you're mainly talking about the girl gamers, I think it's just the fact that wow a girl plays games that's unbelievable to guys for some reason.