I never said it wasn't? Email often ends up passing through other servers you or your counterpart don't control. You could in theory have it communicate direct

I never said it wasn't? Email often ends up passing through other servers you or your counterpart don't control. You could in theory have it communicate directly with your counterpart's server over TLS, which would provide a good deal of privacy, but then you're trusting your counterpart's server. Given that most people aren't capable of running a mail server, it's not an ideal solution.