That can’t be the issue. YYR is a 2 hour flight from EWR. EWR is awash with aircraft, pilots and flight attendants. In a emergency which a aircraft on the ground in minus 30 temps certainly is you simply cancel a revenue flight or two depending on what is available and dispatch those aircraft to YYR. Sounds like someone at UAL made a decision not to disrupt revenue flights. That would be a very poor choice.