The problem in not the airlines its the FAA.

On of the reasons the airlines tend to leave people on the panes is that when ATC releases a ground stop they often give planes a very short takeoff window, I've seen as short as 5 minutes, if they arent airbourne by then, ATC can resind the takeoff clearance, resulting in further delays. So if they go back to gate, and let people off they could end of lengthening the delay by missing a takeoff spot.

The airlines are in a no-win situation.

Too bad some presidental candidate doesn't have a slogan "It's the FAA stupid".