> Because lots of us upgrade phones every couple years, or have dropped a phone and had it break, or get water in it or something.

This is just a matter of using one of the many TOTP authenticators which allow backups of the keys.

If people drop or lose their phones, do they lose all their contacts, photos, passwords? I bet not. I am pretty sure this is a solved problem by now.

Moreover, even if you do lose the keys, that's what account recovery processes are for.