>WhatsApp has been wildly successful, my very non-technical in-laws use Signal for their family's conversations, and other messaging platforms are jumping on the bandwagon.
You only get effective end to end encryption if you can verify that you are talking to who you think you are talking to. Otherwise the people that are running the system can cause your messages to take an unencrypted detour and thus be able to read them. This is often called a man in the middle attack. Verifying identities normally means checking some sort of long identity number. Very few people know how to do that in an effective way.
For example: in a usability study involving Signal[1], 21 out of 28 computer science students failed to establish and maintain a secure end to end encrypted connection. The usability of end to end encrypted messaging is a serious issue. We should not kid ourselves into thinking it is a solved issue.
PGP in a sense is actually better here in that it forces the user to comprehend the existence of a key in a way where it is intuitively obvious that it is important to know where that key came from.
[1] https://www.ndss-symposium.org/wp-content/uploads/2018/03/09...