BA 777-200 SAN

Flight out of SAN on 29 Sept, BA had a 777 parked near the control tower. Usually, they fly in early evening, turn aircraft around and depart couple hours later back to LHR. Just curious, is this a maintenance issue or is BA using 2 aircraft, seems like a waste of resources.

I’m sure it was a maintenance issue or perhaps a cancellation for some other reason.