With email being the source of identity on the internet, it's really unfortunate that the standards have largely lagged heavily behind when it comes to stronger

With email being the source of identity on the internet, it's really unfortunate that the standards have largely lagged heavily behind when it comes to stronger authentication algorithms. Why is SMTP still plaintext on port 25 for MTA<->MTA? Why is STARTTLS really the best we can do? Why do we not support 2FA or mTLS or passkeys or any one of the other modern authentication mechanisms or IMAP4, SMTP, etc.. ProtonMail is ok but the hoops they have to jump through to get their stuff working is obnoxious.