The capacity of the lounge isn't particularly high, so I imagine if you get a lot of long-haul flights going out of particularly B gates - or subject to delay - you might see a short-term uptick as people use it as a glorified waiting room. If you checked again in 30 minutes (currently it's still a highly percentage occupancy) the picture might well look very different.

Either that or those "eligible AA customers" have suddenly found a way over from T3 and have swamped the place.