Majority of TikTok's user base watches what TikTok decides to show them, which TikTok can optimize to lower their content creator payouts (and further optimized by only showing content that have been properly primed in the CDN). TikTok's monetization is also pretty nebulous and also terrible; Youtube's "bad" monetization rate is like $4 CPM, TikTok's is allegedly $0.001.
People choose what they want to watch on Twitch, which they have to pay as a portion of subscription costs to the channel.
No, I've just worked with Twitch and had friends in executive positions at Twitch. Many of their top streamers that pay the bills for Twitch are recruited and have employment/partnership contracts. They're very much paying for content during the time I had connections with them (pre-Amazon and a while after).
The nobodies that no one watches doesn't cost or earn Twitch very much.
People choose what they want to watch on Twitch, which they have to pay as a portion of subscription costs to the channel.