None of the three items I mentioned involved scale. Two of them mentioned cost to host and one mentioned advertising the creators’ work.
The CEO of Nebula has explicitly stated he isn’t creating a YouTube competitor. Nebula has a paywall which is important to its business model. It could never afford self hosting for free.
Even if PeerTube solves the hosting cost problem, you still have two advantages that a YouTube like system has over a PeerTube like system.