Mostly, it will be instances blocking troll and hate instances. But the line of what is acceptable varies from one instance/admin to another. The instances on the top of this list most likely just have a lower threshold for tolerating shitty behaviour
It might not necessarily be that the instances are stricter, it could also simply be that those instances are targeted more often by hate/trolls so interact with those instances more often. Admins are less likely to defederate from an instance they've never seen or heard of. I see a lot of obviously LGBT-related names in this list which likely get more hate than average.
It might not necessarily be that the instances are stricter, it could also simply be that those instances are targeted more often by hate/trolls so interact with those instances more often.
It's both of those things IMO. Being stricter comes about because of being targeted more. It's not always just responsive reactions to abuse. Often it's pre-emptive defederation even before abuse is received, just to ensure it never happens. And that's the part where "stricter" comes in to it, because a lot of generalist instances are happy to respond only if and when another instance becomes a problem
At least, that's how it works on the queer instaces I admin :)