Two-factor authentication, why a backup mobile phone and no other options?

Two-factor authentication, why a backup mobile phone? Personally, I have one phone. I don’t and won’t call someone and wake them up to give me a code, not even my wife.
Why not an email address like the one that is associated with my login credentials? Would be nice if there were more options.

Hi Frank,

We require two phone numbers are for administrators in accounts since if for some reason the first phone does not work you have a fallback otherwise you will be locked out of your account.