I think the only reason people know about email supporting multiple providers is because its old, if email was made today, you bet its going to be centralized. Heck people already scratch their heads when an email isn't hosted @gmail.com or @hotmail/outlook.com. And the learning curve exists because unprofitable companies like Twitter and Reddit made centralization possible by burning money, the old internet was dece…
> Heck people already scratch their heads when an email isn't hosted @gmail.com or @hotmail/outlook.com. What people? Are they in the room with us right now? Anyone that works at a small/medium/large company has an email address @company.com
I've always used a custom domain for my main email addresses and whenever I've had to give it to someone else verbally it inevitably leads to some amount of confusion. At the very least they get thrown off by the fact that I didn't say gmail/outlook/yahoo after the @ and I have to repeat the domain name.