On some airlines, it could be a medical thing. Sometimes a patient lies on a stretcher surround by curtains, usually accompanied by a nurse or other medical professional. I've seem this on European airlines, but never (yet) on a USA legacy carrier.

On AA, I'd assume crew rest, but typically pilots get these seats in business class and I would expect the ones for FAs to be at the back of coach (or in business class if there are open seats).