UA dropped the route because it was loss making. Even with all their feed they couldn't make it work.
Can we knock this myth on the head please? Unless you work in the revenue department at United you can't say that for certain. The best we as laymen know is what the airline itself said: that there are more profitable opportunities elsewhere in the network for the use of a 757 airframe. They've been saying that even since the days of full-tier APD:
Q190 Oliver Colvile: Forgive me—I have heard your argument—but why are you continuing to operate the service? What is in it for you? ... Bob Schumacher: Profit. Q191 Oliver Colvile: But you say you are making a loss, though. Bob Schumacher: It has been profitable.
House of Commons - Northern Ireland Affairs Committee - Minutes of Evidence