@Henry there are instances that really everybody wants to block at a server level, because they aren't sending any kind of useful message but just plain, uncontroversially, spam.
Our instance only has less than 10 active users and no open registration, so we can afford do be very permissive, and we still have a blocklist that is mostly filled with those.
Then there are instances that have been created with the explicit intent to host people accounts dedicated to harass other people: one may prefer a place where these are blocked in advance or one where blocks only happen after the fact, but while under active attack you don't really want every user on a server to suffer from them either.
And then there is simply the fact that some user will want to manage their own block list, but others are much more happy knowing that an admin *they trust* has done most of the work.
The point is that the fediverse gives you the choice to be on a server where you trust the admin and like their policies, removing instance blocks from everybody (or enforcing them for everybody, if it was technically possible) would make it worse, not better.