2 reasons...
1. Ops probably kept telling the crew, "it'll be just another 15 to 20 minutes".
2.The crew is getting paid by the hour. The crew probably didnt "push" for a gate too hard.
The ground stops to DFW that day were hour to hour. When you neared your expected release time, they'd update it and tack on another hour. We went through that for about 3:30 after pushback in STL and finally threw in the towel.
The big problem with an exit strategy in this situation is getting a get and a ground crew (ramp and agents) to work the off schedule aircraft. AA has cut station manning to the bone based normal operations on a CAVU day. Throw in some nasty weather and numerous diversions and the result is pretty predictable. If AA had a plan to handle this, it wasn't a very good one and it appeared to be non standard station to station. After all, winter weather isn't exactly a new unpredictable phenomenon that you can't prepare for.
In regards to pay, I don't think many crews would sit in an MD-80 cockpit for 15 hours under those conditions, paid or unpaid. The truth is that to get paid for ground time during a divert, the Capt must petition his chief pilot for the time less 20 minutes for refueling. Additionally, most crews that day pushed some FAA legality that resulted in them being unable to finish their sequence as scheduled and would lose significant time as a result.