I think the problem is just the massive storage costs of holding lots of video. Youtube is king because anyone can upload whatever, at any amount, but instances of peertube have to monitor their usage closely.

I was uploading to one only for vtubers, and they said they had enough money for 6months or so without dono help, but one month someone attacked or something and just ended up consuming videos at a repeated and huge enough rate that they got a surprise bill that was just too high. They also near the end had to turn off better streaming encoding because it was bandwidth heavy.