And why does that matter, please?
If the author is arguing that 'mail is easy now' you can't make that argument without addressing the security aspect. I hate google and I still use gmail because their project zero team is so good.
Big consumer tech companies are finding their own ways to make this argument: apple with privacy, google with security research, even facebook with providing better privacy controls, although this isn't in their DNA and they'll fail. More products are supporting MFA/FIDO now.
If 'mail in a box' etc are going to convince me to self host (which I would love to do), security is the missing piece.