Not disturbing the planned schedule and expected arrival time of a planeload of passengers? Or is it about getting 65 passengers to Cleveland with less disruption to them? Or are you suggesting there was a better way that would satisfy these both ideals with some cost that UA was unwilling to incur?
There's always the option of flying an extra section SAN-CLE. Or an extra section on IAD-CLE the next morning - UA definitely had enough advance notice to organize that. What it comes down to is that UA is too cheap to consider such alternatives, because it doesn't understand that the revenue premium it commands from offering a nonstop is contingent on the flight actually being flown
without stops.