Yes, Hack Liberty closed their Matrix and Lemmy instances. Their forum post presents some alarming things on Matrix, but its Problems with Lemmy section consists only of few paragraphs on "federation issues" allegedly being the same as on Matrix (Wrong - not much of Matrix criticism is applicable to Lemmy), defederation and problems with entire Reddit/Lemmy/Tildes/other social news aggregators
PewDiePie posting on PeerTube will result with many of his videos being viewed on PeerTube. But either:
he would make an instance only for himself and majority of his viewers would fail to make a Fediverse account to follow him, or
he would open that instance for his viewers to make a account there, but then he would be liable for every comment made by his viewers, or
he would make an account on already existing instance, making a great burden of moderating his viewers for existing administration and moderation team.
An entire network cannot be effectively marketed and accomodate a new users' wave as well as any centralised website, like YouTube, or Bluesky.
You might like https://piefed.social.