I don't know if it's that. It looks to me more a consolidation of their "old" services (ABZ/GLA/EDI) and the bmi equivalent for the sake of simplicity. It's easier for passengers if routes are delineated along the lines of of "flying to EDI go to T5, flying to BFS go to T1" then "flying to EDI on BA XXX then go to T5, flying to EDI on BA XXX go to T1" etc.

It's a lot easier from a point of view of scheduling and aircraft positioning for BA too I'd imagine (as by that time all the bmi operating will be finished with, and the aircraft and crews will be BA ones).