Lots of email servers support fallback to non-encrypted, plaintext transmission, which can expose entire chains of replies to MITM attacks with a single message being routed questionably. [0,1,2] End-to-end encryption, via user-defined keys is actively discouraged by those who might assuredly know better, and be in a position to change minds. Usually, the cop out comes in the form of "too complicated for non-technical/less-technical users, and thus potentially harmful to profits."
As if to say, we've been espousing the use of an insecure method of communication for decades, so, to suddenly reverse our position, and encourage bring-your-own-encryption might provoke discussions of liability, or something. Nevermind, the premise of ad tech and scanning user messages, to sell data.
But you know, running your own server, and hiring people who can't be bothered to go deeper than using word art in MS PowerPoint slides, well, hey. Bring a horse to water... know what I'm saying?
PGP is easy to use. At this point, I'd like to think people are fatigued enough by the bottomless pit of nightmares we've fallen into, that they'd step up and tell people: yes, people are using SSH keys and SSL keys billions of times a day. It's okay to use PGP on your email. Go ahead, start doing it.
Or, you know, whatever. Lose another election. Right?
[0] https://en.wikipedia.org/wiki/Email_encryption
[1] https://blog.filippo.io/the-sad-state-of-smtp-encryption/
[2] https://security.stackexchange.com/questions/51552/how-insec...