I think the key issue is being able to fail over to another video site if for some reason YouTube decides you're no longer the kind of creator they want. For Rossmann I think whatever ad-revenue he gets is pocket money (and I believe it's not a lot in the great scheme of things), he already has a functioning business that's revenue generating.
Also what guarantees are there when you come along and upload 10+ TB of archive footage to Peertube the network decides that's far too much? Their creator sign up page has an instance filter for "At Least 50GB" (which is quaint). And sure when you get the results back many instances say "Unlimited" storage, but there's "unlimited" and "get lost".