I use twitch for one thing and it's literally to help support a friend of mine. He streams as part of his job to make money. You can't currently do that on other websites and get the same benefit.

I have never liked twitch but I have a pretty valid reason for using it. He wouldn't reach the audience he does there anywhere else except YouTube who don't pay much if anything for streaming and take a more significant cut of donations.

People won't leave because the viable options aren't giving the same benefits, and it's not just about the viewers, but also the content creators.