I think you are missing the point. Comparing BMI and BA- who has a huge international network? What would you concentrate on on ? crew and aircraft (including diverted long haul aircraft) in the wrong places, If you have alternatives methods of travel ie excellent intra UK train links (operating with minimal delays), coach and car then they can concentrate all the efforts and crew on long haul flights. I dont think there is any conspiracy against shuttle flights. Just common sense. A bit like just gritting trunk roads.
Not specifically criticising BA here but what about the passengers that are supposed to be connecting to these long haul flights? Will they wait on the train to arrive? It's a bit like gritting trunk roads but closing some junctions on to them.