Content creators. It’s hard to host everyone’s videos, and it benefits monopolists to imply that doing so is necessary, as it prevents new entrants. It’s not nearly as hard to host your own server (or pay for it to be hosted). It becomes harder when you suddenly become popular, a situation which Peertube explicitly compensates for by sharing the distribution effort between viewers, which scales with popularity.

Signal makes it’s own bed like YouTube by being a single centralised server for everyone. Nobody ever asks “who pays for the servers” when it comes to Matrix or XMPP