Ask HN: Why don't many video hosting companies adopt PeerTube or P2P?
I have some experience with large-scale CDN I've cofounded some years ago.
The short answer is - the perceived benefits you'd receive doesn't match the decrease in quality of service. So the economics doesn't work. 
Content distribution is widely skewed towards 1% of content makes 90% of traffic nodes so the cases that p2p may work for very popular content but the long tail is not easily cached/served. Try to watch/download a torrent file with small number of seeders and you'll get the experience you will be providing for the end user. Also internet networking is tricky and connectivity in different parts of the world can differ widely. South America or Asia have almost none of the peering hubs infrastructure that is available in Europe.
(I've cofounded a CDN company and have some knowledge of the market)