The UA situation is based very much on the need to fill seats ex LHR. They have five flights a day ex LHR to EWR to fill in an overcrowded market which offers no fewer than 30 flights a day to EWR and JFK. The similar markets to Manchester in other parts of Europe do not have that sort of competition, and especially do not have the airline trying to keep slots at the premier airport in the same country, even if it means flying partly full aircraft, whilst the regional airport which had previously performed well enough to fill a double daily schedule and is filling its current seating capacity, is ignored for upgrades.
UA no longer have connections at LHR connections ex MAN!
If UA were pulling such volumes away from MAN they would address it since Red exited MAN-LHR
Only FRA, MUC, DUB, BRU, YYZ are offered.
I accept LHR generally is a factor but primarily in winter and not summer. UA can fill 3 daily ex EDI but only 2 daily ex MAN. While EDI is a better place to visit
MAN should have much higher demand outbound.
Two things - UA are making significant profits ex MAN and they are able to allow for example when DL enter JFK and AA placed larger aircraft or UA are not making enough to justify additional capacity and other carriers have squeezed them so much that NCL-EWR looks more profitable for them to name one.