I'd guess "moral indignation" based on the above, and more power to them, I say.

Though I think nwff has the right of it. This is an area where an ounce of transparency would be worth a pound of cure. Anybody who's flown for more than 15 years will keenly remember when the airlines took responsibility for their failures, whether it was really their fault or not. Now the pendulum has swung to where they refuse to take responsibility whether it's their fault or not... and done everything in their power to mash any and all failings into those "grey areas" where it's tough to pin them down factually or legally.

OP, I'd focus on the GAs leaving the scene and the general breakdown in customer service here. Throw the lot at the DOT if you feel like complaining to a higher power, but the former is your best bet at squeezing any compensation from UA. Otherwise, be satisfied with the $5 or so in lost-productivity, and $0.01 or so of lost public goodwill, that responding to your DOT complaint will cost them!