Part of the difficulty is that email is a federated system, unlike WhatsApp. Adding end-to-end encryption to a federated system, if it wasn't there before, is a lot more difficult than adding it to an ecosystem that you control in its entirety.

I understand and agree with this. That's why you cannot single-handedly add a feature like Protonmail's, without risking of breaking someone's workflow. I probably have myself some GPG key uploaded on some public server, tied to i-dont-even-remember-which email address of mine, and when I did that I surely didn't expect or imagined that some provider would pull it automatically to encrypt every mail in which I'm the recipient sent by their systems.

I understand Protonmail's approach but I also understand - and share - OP point of view.

That's the thing though, you almost certainly at the time expected people to use it, and then a decade passed and nobody showed up. The problem isn't that you did it, the problem isn't that they used the information, it's that you were an early adopter who forgot the passphrase to your bitcoins. You put that key there because you wanted it used, you don't get to pretend that you've stopped wanting to use it and everyone should totally know that because you haven't used it.

You have a sign out saying encrypted email here, and are mad someone finally read it.

Remove the sign, or change it to foo+secrets@mydomain.com

Op is mad he left the sign out saying come in and play when people came in to play way after his party ended.