Why is 2.4.7 Focus Visible Level AA and not Level A?

[doubletaco]

This has been gnawing at me for quite awhile. Why is 2.4.7 Focus Visible a Level AA Success Criteria?

SC 2.1.1 Keyboard states that all essential functionality must be able to be accomplished via keyboard with no specific timings for inputs. However, without a visible focus indicator it would be an arduous task of trial and error to determine what is about to be activated. This places undue burden on a sighted keyboard/keyboard-emulation user.
In a case where focus is not lost, but is not visually indicated (e.g. CSS'ed away) someone could justifiably come to the conclusion that a site was inaccessible for keyboard users.
Hoping to hear some insights, because this is feeling like one of those "Am I missing something?" moments.