No clue as to who made the decision or the reason. United (at least at DEN) is responsible for ordering and coordinating wheelchairs for their passengers. I believe Progress is the contractor. You would think that essential service contractors *should* have a clause in their contracts to provide services during irrops.
I saw five to six wheelchair passengers in SEA, they were waiting at the gate in DEN and I overheard a conversation from the gate agent that services were not available due to the hour. From my walk to the train, I saw no chairs heading toward the gate.
SFO 1K may know more about the policies and procedures since he is an DEN Ambassador.
DEN
At DEN the airlines contract with various providers for wheelchair assistance. United uses a firm called
G2. It is impossible to know from this if the contractor's management released their personnel to go home, the personnel refused offered overtime or United released them (least likely IMHO).