What if you lose your phone? You would essentially be locked out of your accounts unless there was some way to disable it without knowing the 2FA code.
Take a print screen of the QR-code as a backup when enabling 2FA. Then you can use this to configure your new phone.
Wouldn't this essentially make this screen print/picture essentially as good as your password? If someone were to get a hold of this screen print they could essentially configure their own phone to be a 2FA device on the account.