There isn't really anything wrong with these stereotypes because flamboyant gay men and butch lesbians are a big part of the gay community. Not only that, but they usually have to deal with the majority of homophobia and abuse. There isn't really anything wrong with these sorts of stereotypes. Whilst it's good if they include masculine gay men and feminine gay woman are represented as well, gay people who don't conform to ideas about how different genders should act aren't really doing any harm at all.
Okay, need to break this apart a bit. It is true that being a feminine guy or butch lesbian and so on is not wrong or a problem, and those types of characters need representation. However, it's dangerous to start claiming that they get more abuse than others; it would probably be more accurate to say that they receive abuse that others don't get, but that doesn't mean a feminine lesbian, for instance, doesn't suffer from homophobia or sexism.
Also, I'll quote Chimamanda Adichie: "The problem with a stereotype is not that it is wrong, but that it is incomplete." Those stereotypes aren't wrong, per se, but there's something very wrong if that's the majority of what we're getting all of the time. We need balance and variety is basically what I'm saying.
Why is it a game developers job to help issues like sexism , racism, or homophobia?
It's not their job, and their under no obligation to do so.
That said, they have the power to help the situation, and if they choose not to do it, then they're choosing to allow those things to continue. We're all in this world together; it'd be nice if everybody did what they could to make it a better place for everyone.