

Haven’t asked the admins, but here’s my guess.
Being the most well known instance means that you get a lot of traffic. Let’s say that 1% of the people using your instance are annoying morons. In a smaller instance that 1% translates to maybe one ban a month or whatever. In a bigger place, it becomes a constant onslaught stupid idiot bullshit nobody has the time or energy to deal with. Either you get a bunch of admins and mods to deal with that nonsense or you start banning users more aggressively. If that doesn’t help, you may need to look at the instance where those troublemakers come from. If you notice that a particular instance pops up disproportionately often, you might want to consider defederating from it.
However, some part of that drama is public on fediseer. Have a look. Just scroll down to censures given and read the reasons why lemmy.world has defederated from so many instances.

I’ve tried reading my local and federated feeds but found little value in them. Most posts are either too niche, too uninteresting or just fly straight over my head. Consequently, I prefer to stick with the subscribed feed almost exclusively. That’s where I can reliably find stuff worth my time.