Its users, in part because it uses web torrent which means the traffic of videos is shared peer-to-peer, thus the host doesn't have to pay for a lot of bandwidth.

Also, just like mastodon servers are paid by its users for service I'm sure admins that build up a good reputation with their users or make them aware that they need more to pay for it will pay, or not and they'll just disappear which is really how the web should work, not all these tech oligarchs who have lots of money from exploiting their users and workers.

Edit: Was incorrect, it uses HLS with P2P support:

At the beginning of PeerTube, we only supported Web Video (previously known as "WebTorrent") streaming. Due to several limitations of the Web Video system, we had to add HLS with P2P support.