A single admin on a larger instance could get a stick up his ass and defederate a smaller instance, which would then propagate to everyone else copying that ban list. Power tripping admins didn't die with Reddit.

that's exactly where shared blocklist are a problem, if for some reason or another someone's instance get mistakingly defederated, which is far form unlikely in one the enormous instances that have to manage federation of hundreds of instances, then all of a sudden, that big instance everyone trust get their blocklist copied all over the verse and poor jane is blocked from everything and has no idea why

They could have done nothing, but because someone on a so called trusted source de-federated it because he did not like him, de-federation would accumulate.

Actually beehaw is a nice instance and is blocking lemmy.world, which too is fantastic. Thus sharing beehaw's de-federation list would cut out lemmy.world from a huge audience. In this particulare case, I wonder what lemmy.world did wrong to be worth de-federating from.

So you see, sharing huge block lists would wrongfully cut out people. Since nobody would investigate the whole list because doing so would take weeks.

Joining another instance is out of the question for many because they are firm belivers of self-hosting and decentralization. Two principles that are pillars of the the fediverse.