Martti Malmi on Nostr: What attack does the symmetric ratchet protect from? If your device is compromised, ...

What attack does the symmetric ratchet protect from? If your device is compromised, your message history will be revealed anyway.

Maybe it would help in the case when you locally delete earlier messages in a chain ("disappearing messages" or otherwise) but they're still on relays.

Maybe I answered my own question, but is there something else besides this?

Why not more difficult? Implementing DH + symmetric ratchet is more complexity than just DH.