This is an argument for standards. You can switch messaging clients. Platforms own you.
I know some very privacy-focused person (a friend of mine) who will stop being willing to be in contact with you (or being your friend) if you use an email address at one of these big spying email providers to write him an email.
So, it is just a matter of being consequential.
It was an X.400-based nightmare, and never took off.