They've defederated from a Iot of common badfaith instances on the fediverse, lot of pleroma and masto troll/fash instances - which is normaI for admins on the fediverse. Its active protection of your users from harrassment. Most mastodon instances have 200-400+ instances blocked and defederated. Its standard.

Lemmy admins may be new to the fediverse, but once the troll instances start to realise how easy it is to mess with you from the safety of their instances, you're going to need your admins to start communicating with the long term masto admins, get their blocklists and recognise how they keep their users safe proactively rather than retroactively.

Defederation is one of the strongest defenses the federation has in terms of maintaining stability within its wider network and enforcing that admins/mods do their jobs. Its a matter of everyone seeing eye to eye and agreeing on ground rules for civility and agreeing they're going to moderate to a decent active standard and keep control of their users. If an instance is unable to keep control of its house, or the admin goes AWOL and ends up with tons of bad faith users running amok flinging poop everywhere, then yeah they will get defederated. It can always be fixed later on with serious discussion and commitments made between the admins of instances.

But yeah every instance on the fediverse that doesnt want underage porn / nazi imagery / fascist agitators / gore / hatespeech etc getting posted continually to their users, is going to have to defederate a couple of hundred instances. The Fediverse is a lot bigger than Lemmy, and people outside of Lemmy/Kbin can all post to your instances and your threads, or even start our own threads.