You seem to operate under the presumption that content and culture generally can only be created on major platforms. Nothing stops creators from finding other spaces to post their content. It's what sub-cultures have done pretty much throughout time -- find alternate spaces to explore ideas that might be outside of the mainstream.
It's not like Spotify is sending hit squads out to shake down artists that don't join the racket, or harass studios and sites that host content they disagree with.
There is a lot you can do with a big microphone, but perhaps the Internet isn't and never will be the utopia that people imagined it would be. In a different world where large tech companies were completely hands off and governments embraced a speech free for all, many people will still feel that they don't fit in mainstream spaces and will need to find another forum.