Aside from what others have mentioned I feel like it has to do with identity. Young kids really want to stand out, we've all been there, god knows I had my phase of I'M ORIGINAL. It's especially so because, I dunno, it deals with sexual identity which is probably one of the most personal things for anyone.
So obsessed with identity it's a wonder you keep seeing so many pseudo terms obsess over every nonsensical nuance to someone's sexual preferences, or the gender they identify with, or whatever. Of course this is all just an uninformed opinion, so take it will a grain of salt, but so many shades of tumblr sound like a bad RP profile.