Historically, people value low cost and convenience over any other feature. Unless there is some GDPR like directive requiring decentralization and self hosting, it will likely stay centralized and become even more so.
Many people still use aol or their email given by ips or work email domain.
Worldwide yandex.mail is popular.
Colleges still give email addresses.
People like myself run their own
Vanity domains are popular.
Mail is still decentralized and news of its death have been greatly exaggerated
The significance of "originate OR terminate" is that the provider has the ability to meddle or outright ban, either going out or going in.
> work email domain.
> Vanity domains are popular.
> Colleges still give email addresses.
Most universities, workplaces and vanity domains are running within the Google+Fastmail+Microsoft sphere, regardless of the domain name. Every university I've worked with in the last 10 years (e.g. NYU) was using a G-Suite or Microsoft hosted solution, as was every single workplace.
> People like myself run their own
There is a very long tail for the last 1%, but likely 99% of the users are served by 10 companies worldwide. I call that federated, not distributed.
I used to run my own server as well, for ~15 years. Until one day, google stopped delivering it to gmail or g-suite addresses (sent it to spam). There was no one to talk to to figure out why. Which turned out to be ~70% of email I sent -- despite having SPF, DKIM, DMARC and everything else properly set up. Eventually, I switched to fastmail hosting because I have better things to do with my time than figure out why Google is blacklisting me.
It's federated, not distributed, and we're all at the mercy of the big few.