[tptacek]

Messaging applications use protocols derived from Signal Protocol rather than PGP because they had the opportunity to do something better than PGP. The first secure messengers did use PGP; designing a new messenger based on PGP would be malpractice.

WhatsApp uses Signal Protocol, and protects many order of magnitude more messages every day --- or, if you like, bytes of plaintext --- than PGP ever has or will.

Email not being a messaging protocol is... a take.