This actually could be done by anyone since PeerTube uses WebTorrent. Good samaritans could run a webtorrent-hybrid or WebTorrent Desktop instance and help serve those videos from their home connection or personal server(s).
While it's what we usually do when we uses BitTorrent and similar protocols, this is ignoring network topology, and somewhat inefficient. Of course, theoretically not the global bandwidth, but the pipes congestion.
Home connections are not connected to the internet, but to a service provider connected to the internet. Home are behind distribution trees connected to the internet graph.
Nothing forces ISPs to optimize routing flow inside their AS to distribute content. Could be at their root tree. How can we expect people with capped upload speed and high latency to IX servers, while some global CDNs are already closer to homes on ISPs regional level PoP?
And besides, traffic shaping, throttling, protocol blocking on private ISP infrastructure is now unregulated in some parts of the world. Massive outbound traffic could unbalance their (massively inbound) peering contracts, this is a threat.
The principles of free, open and decentralized internet do not necessarily apply to users of ISP infrastructure.