Give the OP a break please
BA dont like to re route on non OW carriers we all know that, there are only 2 flights a day out of PHL in the evening and the OP was on the later one which is a 767, this flight is sometimes cancelled, seemingly at random, in 9 years of flying from PHL this had happened to me a few times.
The only AA domestic connections from PHL are DFW, MIA, ORD so ORD was given as the logical choice. You do have to ask to be routed via EWR as you have to make your own way there,its only a train ride from 30th ST but it doesnt show up on their system as no AA connection