Mainstream isn't always the bands fault, nor a bad thing. It just means popular, and if a band get more popular, so what?
HIM may not be mainstream, but they're already styled in the perfect way for their audience. They're sort of 'goth', and that fits their little fans just right. I'm guessing it's the little people like you who do treat bands like HIM that way. Something that fits their image. That's just as bad as the idiots who follow the mainstream. The little goth kids think because it's not as popular with these mainstream fans, they're different, when all they're doing is the same thing in a slightly different way, with a different look. A look still shared by thousands of other people.
Damn it, I hate goths!