Convincing somebody who can hardly turn on their computer to get their own domain is just not practical. Even if they can get their own domain they still have to set up DNS. Good luck getting them to set up MX, spf and dkim.

I think things would be better if more people had their own domain. I just don't see any way of making it happen. I can't get my own family to leave gmail even with me handling all the domain stuff for them. Even my technical coworkers who are capable of this don't care.