Why wouldn't they just embed the hash of the message, or even the hash of a chain of messages? (AFAIK people have been doing this for a while for other applications).

There was a much more sensible attempt at this with bitmessage [0] but anonymity and security guarantees are hard, and everyone receives everything is a really expensive strategy for a messaging protocol.

tl:dr those that don't research prior work are bound to create useless stuff.

[0] https://en.wikipedia.org/wiki/Bitmessage