I don't really understand this logic. The fact that they make more money somewhere else means that they should have to somehow give that money to Twitch as well? If Twitch isn't set up to be able to make a profit from subs and bits, that sounds like an issue with their business model, and they should find a better way to monetize users on their site. From some very basic searching, it looks like there are NBA, MLB, and NFL players who stream on Twitch, as well as professional musicians and actors, and I imagine most of them aren't making the majority of their income on Twitch either, so should Twitch be trying to get a cut of their product endorsement deals and other sources of income that come from being famous?
I'm not saying you're necessarily wrong that that Twitch is losing money on them, but I don't really see how that's something specific to one type of streamer. If the issue is the ratio of subscribers/donations to the number of people watching those streams, why not just make policies about that specifically, like putting limits on how frequently someone can stream after a certain number of hours without having a certain amount of revenue either via subs/donations or showing ads? I think they'd make much more effective strides towards profitability focusing on stuff like that.