> SMS, to me, feels like a way less secure, less functional, less portable, and more expensive email.
You can't port email addresses unless you own the domain. For the majority of people SMS is the more portable option because they can freely port their phone number to a different carrier.
"portability" probably refers to being able to access messages from multiple devices, which can be easily done on email but not text messages. People port their phone numbers to get a better plan, but that's rarely done for email. At best there's a handful of privacy conscious people switching gmail for protonmail or whatever.
Everyone just uses Gmail/Hotmail/iCloud/Proton which just don't have the port problem as carriers because you don't have any reason to port since there's no fees and no physical network, you can just accrue more and use mail forwarding with no problem.
that's another cost, have fun getting your emails dropped by microsoft because they don't like your ip addresses unless you pay someone else to send for you
You can't port email addresses unless you own the domain. For the majority of people SMS is the more portable option because they can freely port their phone number to a different carrier.