Some of the instances choose not to federate with others. For example https://tilvids.com/ Here they explain why: https://mstdn.social/@tilvids/106902477087882284

I'm not sure webtorrent have a way to do peer exchange without centralised trackers like e.g Bittorrents PEX does, so if the core websocket trackers go down, are peers still able to share lists of known peers with each other or is the peer discovery centralised to the webtorrent/websocket trackers?