One example is the lemmy.ml problem. You see the rest of the Tankie Triad is pretty widely defederated from, but lemmy.ml isn’t despite doing much of the same things, just a bit more subtlety.

Because lemmy.ml is such a big instance and has a few of the biggest comms (By subscribers only, which means a bunch of dead accounts boosting the numbers, by MAUs a much different story unfolds) many instances admins are hesitant to defederate from them

Big instances carry too much power and influence and if you’re a toxic instance like .ml, it can be used to basically bully other instances into remaining federated with you