It doesn't, but 59/17 do quite a lot through gift wrapping. Payload size, creation time, and all tags (including author) are hidden except for recipient, which can be obscured through key exchange.
nostr:npub1jlrs53pkdfjnts29kveljul2sm0actt6n8dxrrzqcersttvcuv3qdjynqn how does nip44 improve metadata hiding?
Discussion
If DM or encrypted data is so important and unique, why don't we just have a totally different format for it instead of following NIP-1 format? What if we design a better format for encrypted data from ground up?