I remember reading a few years ago in one of BA's flight magazine that Belfast Aldegrove was one its main hubs along with Heathrow, Edinburgh etc. As Im sure you know Belfast Ald is no longer a hub to BA or even a destination. If I am not mistaken the last flight out of there was the Birmingham route. I am not sure how long they will last down at the City airport as well. They must only have Manchester, Glasgow and Edinburgh left.
You could say the same about my local airport Newcastle as well. We used to have a major regional hub up here now we have a little skeleton service and with rumours circulating about the future of the airline at the airport uncertain who knows what will happen. I suppose as long as BA keep the rich people from London and the South East happy then BA are happy.