[elahd]

I figured this was:

1) An experiment to test the level of familiarity that non-technical users have with two factor authentication. That is, does a person who incidentally enabled SMS 2FA understand that having to enter an SMS code every time they log in is a pattern called "two factor authentication" as opposed to just some weird part of Google's login workflow.

2) An artifact of a user's security preferences living in a protected space that can't be accessed by Gmail's frontend. Gmail's dev team got an order to encourage users to enable 2FA and this is the best they could do.

3) A ploy to get people to review their 2FA settings -- or to be sold Titan Security Keys. Google's security team has sent me several emails over the past few months encouraging me to buy these, claiming that I'm at an increased risk of a targeted attack. I'm not fully bought in to their motives.

(All conjecture.)