Just looking through the settings they have stuff which would have no obvious automation angle. The reduce transparency option for example, the noise recognition feature to alert you of fire alarms, pairing with hearing aides, etc. Tim Cook said himself in an interview that they provide accessibility features regardless of ROI.
That's not the initial point. The point is that UI tests are so much easier and less brittle if they're going to be using the accessibility tree, rather than relying on a few selectors.
click("Enable Frobzinator") is infinitely more maintainable than click(button().index(7)), and if you eventually remove the accessibility description, your test fails, letting you immediately know what's wrong, and whether it's the test no longer up to date, or if you broke something.
