The explosion of MFA in recent years means that every consumer on the Internet is also inextricably intertwined and dependent on their phone number. They may not even know how to change their phone number in all the profile settings of all the accounts that send them an SMS code.

Losing control of your phone number is no longer a mere social inconvenience. It is a disastrous disruption in your authentication flow, and could render a portion of your online accounts completely inaccessible due to inadequate recovery processes.

There are frequently no paper backup codes or secondary options for people who use SMS MFA. Lose your number and you lose those codes. Good luck recovering from that.