Focus
SC 2.4.3 - What does "Focus Order" mean?
You tab through a form. Name, then email, then suddenly the footer, then back up to the phone number. Nothing is broken exactly. Every field is reachable. But you have lost track of where you are and what you have already filled in.
SC 2.4.7 - What does "Focus Visible" mean?
Imagine filling in a form with your mouse, except the cursor is invisible. You click somewhere and hope you hit the right field. Nobody would ship that.