I have been out of BA for almost as many years as HZ123 has been in there. When I was there, I was responsible for the commercial planning of the US routes, including the ‘Provincials’.
They have some particular features. Basically a daily East Coast rotation can be flown with a single aircraft, giving a very high utilisation (good thing) but if anything goes wrong, mechanical problems or other long delays, you’re in big trouble. Also, the aircraft has to be returned to mainbase periodically for routine maintenance. Ferrying aircraft and crews backwards and forwards between LHR and MAN can wreck the economics of the service.
Also, in my day, the provincial routes were much lower yield than LHR. Story was that BA was forced to maintain a wholly-uneconomic FC product at the insistence of Sir Harry Pilkington (the St Helens glassmaker) whose company provided the airline with a lot of business worldwide, and who insisted on his creature comforts on MAN-NYC.