Because the main point of Reddit is that there is a moderator deleting stuff that doesn't apply to the community. It's curation at its best.
Discussion
Some of the best subs are the ones that are very lightly moderated though.
What happens when community tags get orphaned? Can the tag short name (I.e. a/communismbabble) be reused my multiple communities? Since communities could be subscribe-only, and nobody else would see them unless their subscribed, they could be subscribed via their pubkey and the community 'handle' could be used by many groups. This would avoid people squatting on handles, and if someone dies without adding other moderators/owners, the community can simply move to a new pubkey. The only wrinkle is when a client is subscribed to more than one community with the same handle, but you should already have a UX solution to this for npub/username conflicts
I'm here for it! Nostr is the best place to create systems for distributed moderation.