Prior to the merger with US Airways, American Airlines crew would generally stay together on a trip and even stay on the same aircraft. When a flight delayed, it was only that flight and crew which were affected (and subsequent flights scheduled with the same aircraft).
US Airways management took over and eliminated this practice. When a plane lands at a hub, crew disperse on separate journeys. When a flight delays, that means each flight attendant and pilot going their own way delays a flight. There’s a cascading effect on the operation.