I believe they also used to operate MAN-LAX and dropped the route due to poor loads.

The loads were decent enough (some 110,000 pax over the 18 months or so it operated), but the front-end of the plane may not have been overly-subscribed. But throw into the ring “the BA shuttle service” and the “hidden” encouragement by BA for the premium pax to go via LHR and you can see why it wasn’t destined to last; I believe the BHX-JFK was similarly handicapped when they changed it from 767s to 757s which probably affected cargo carrying capability which might be able to mitigate the lack of premium payers.