https://en.wikipedia.org/wiki/Joost
The cost of delivering content is not zero. The main variables are the codecs & quality of a stream, which on average is going up, and the cost to deliver (bandwidth/storage). The cost deliver keeps going down.
So, there are periods of time, when a p2p approach "looks" nice. 4k? Maybe all this live-streaming stuff? Sure. But what happens is the cost of delivery with HTTP keeps going down.
Joost had a bunch of other issues that made it fail, un-related to the use of p2p.
p2p might be cheaper to operate for a business, but it has almost no advantages for users over a well built CDN. For users it only has negative attributes (baring a few situations on LANs / getting streams into places you can't put a CDN).