Nope, just saying phone numbers are far from the only option.
What would you think would be an appropriate alternative to easily verify chat accounts that’s cheaper than validating phone numbers?
It’s the cheaper portion that’s the issue. There are “other options”, but they’re not cheaper and/or they have their own issues.
I didn’t touch the email case because email addresses can be so rapidly created (even out of thin air via a catch all style inbox) there’s nothing to it.