There is a legal basis. US can ban Russian Times paper, too.

They are probably trying to find that spot where it’s just slightly more annoying to block ads than leave them unblocked.

That’s still a person against a bot. Spammers can spin up accounts automatically in Nostr with no verification.

Nostr has its own problems. Like you can’t easily defederate from spam servers in Nostr. Every person has to remove spammers, too, instead of an admin doing it.