At least as I remember from DFW local news sources, the "large" renewal order for narrow bodies was set to be all Airbus. Boeing got wind and managed to convince them a new order for the 737-whatever had better financials for the "middle" narrow-body capacity than a new order of A320's. So now the legacy al A320's are the orphan fleet rather than the legacy 737's.
But the other rumor that never went away in local business circles was that AA had really wanted the stretched 717.