People are very particular about their music. Doesn't it make sense that a service built for niche genres doesn't have broad appeal? I fucking love soundcloud and they nailed their product years ago, so I'm really excited to see what deals they've been cooking up the past year or so.
There is nothing inherent in the structure of SoundCloud that limits its usefulness to only niche genres. Mainstream genres simply have access to more established avenues of promotion, like radio and YouTube.
I bought Soundcloud Go the day it was available.