They didn't leave the mainstream channels because they weren't allowed to speak. They left the mainstream channels because truth was not compatible with their worldview.
Go watch the George Floyd body cameras. All of them. The full 1 hour (30 min per officer). The story is ENTIRELY different than the one that was fed to us.
People don't trust those channels because it's so easy to look at literally any other non-mainstream source to see how we've been constantly lied to.