For my upcoming trip in a few days, J was still selling up until a day or two ago.
The question is how many elites are paying attention to the schedule more than the aircraft when booking a trip PHL-LAX where there's a 440pm on an A321 and a 605pm on a 787. Ditto for the red eye back where there's a 1030pm on a 787 and an 1109pm on an A321.
PHL LAX/SFO having a widebody is nothing new. Even before Covid, there was an A332 on these routes.
You are also forgetting than many passengers connect in PHL so this makes it easier for AA to fill the F cabin.