[pmlnr]

That is only one important aspect. It's also provider-independent (as long as you own the domain, that is true) and is, by nature, decentralised. (Like really decentralised, even by redundancy provaded by MX record priority in DNS.)

[emilyfm]

Unfortunately very few people have their own domain for email (although they should!).

When companies have kindly sent me their entire customer list (by using CC in place of BCC) I see there are very few domains in it outside of the major free email providers, and those that remain are mostly for their work or small business. A personal or family domain is very rare.

[alkonaut]

I have my own domain, and I really should be using me@myowndomain but I don't. I use gmail. One reason is that so many people and services already know the gmail one so it's hard to change, but the biggest reason is that I don't trust myself nor the place where I registered for my domain to actually maintain the domain name registry and email delivery for say 10 or 20 years without any maintenance. The value of these behemoth services is that they are more or less guaranteed to be more stable than anything you can configure yourself. They are too big to fail. Even just pointing my me@myowndomain to gmail doesn't help here. It just adds a new weakest link to the chain.

[emilyfm]

I've had domains registered for over 20 years already, much longer than gmail has existed.

You can renew a domain for ten years in advance and easily transfer between registrars (and email providers, I use Fastmail), so it's a lot more reliable for the (very) long term than a third-party service.