Old US had one way to route you WAS-MAD (or most cities in Europe): DCA-PHL-MAD. New HPUSAA has a bunch of ways: DCA-JFK-MAD, DCA-BOS-MAD, DCA-MIA-MAD, and IAD/BWI-LHR-MAD, all of which offer reasonable connection times (and all of which stay within AA's metal-neutral joint ventures, meaning AA gets the same cut of the fare no matter which of these routings you choose).

Given that, it seems like US has much less reason to operate the ridiculous number of DCA-PHL flights that they used to, and considerably less need to feed the PHL transatlantic bank from DCA than they used to. They can feed that bank out of cities that are further from PHL and thus have an O&D reason to have flights.

It would be nice if AA would codeshare with Amtrak and sell protected connections out of PHL, but that's obviously not nearly as straightforward as it is for UA at EWR. That would make a lot more sense than very frequent DCA-PHL flights.

(I recall they had flights every 30 minutes the one time I flew it. The 50-seat CRJ I flew on had 4 passengers! For a route with pretty closer to zero O&D, that makes no sense. I certainly take the train or bus or drive whenever I'm going to DC, as I'm sure does nearly everyone else.)