Using p2p for messaging is really nice for decentralization, but it has the major downside that both communication partners have to be online at the same time to find each other and transmit a message. So you might have to wait for it until both look at their phones at the exact same time. On top there are privacy issues, like being able to see the devices and public IP addresses of other users.

Imo its just not practical and robust enough to be used by millions of non-techy people.