The way the genre came into the mainstream mirrors every other post-1976 musical movement:
Like grunge in Seattle, Punk in New York, London and Brisbane, SoundCloud/mumble rap was based mostly in a specific place: Florida.
It was one song that pretty much brought the scene to public attention: Look At Me by XXXTentacion.
Their style of music and sense of fashion has become controversial.
All of these things add up: I reckon that kickstarting a new musical movement could be easier BECAUSE of the internet. Not necessarily genetically aimed to try and target the mainstream but in general.