Even if self-hosted email was easy, I don't find it to be a great idea.

I ran my own for a while using mail-in-a-box but ended up moving to fastmail because I didn't trust myself to maintain the setup. I need my email system to just work and that's likely the same for the majority of people.

(I validated that lack of trust in myself even with fastmail by not realizing for almost 3 days that I let my domain expire, thus causing emails to bounce with no way of me knowing that was happening)