

Each instance owner is running these instances themselves, presumably out of the home, for free.
They could go after an instance owner, sure, but
There’s no “but”. They could fight a lawsuit, sure, but that’s time consuming and expensive, and why bother? The piracy isn’t coming from their instance, why should they have to fight a lawsuit for it? Piracy has its own instance, nothing has been defederated, they’re just not hosting the content on their server to save themselves the hassle down the road. I can’t imagine they’ll be the only one.
The Sonarr/Radarr/Lidarr/etc team, and their support forums/subreddit are seriously the worst about this. Nearly every question, concern, or request with regard to torrent trackers is met with a smug response about usenet.
Assholes have started exploiting Sonarr’s torrent pulling system to trick it into downloading fucking malware on people’s computers, and rather than acknowledge this is an issue their users are facing and they should try and do something to help them, they’ve done nothing, expecting users to deal with it in their clients and through addons. The implication is if you’re not using usenet, they don’t care what their software puts on your computer. It’s your fault for using public trackers.