How can you be banned from the fediverse?

I understand your pedantic point but let me give a realistic reply. If your account, or the account of somebody you like corresponding with, happens to be on an instance that falls into disfavour (not uncommon in my time there) then server bans come out and conversations become broken, even between parties who had no knowledge of the overarching drama. Good luck even understanding it if you aren’t a techie.