Part of the answer (and also why I don't like most of the ideas people have given on how to fix NIP-04) is explained in this commen#[0]ilger: https://github.com/nostr-protocol/nips/pull/306#issuecomment-1447563490

"There is a conflict between the user wanting no metadata, and the relay wanting to know who to charge or whether to bother hosting the event."

"If public relays are gracious enough to host these, there would be an incentive to game that by storing massive data under these events, and then relays would stop hosting these. I cannot see a way out of this pickle."