I think you will find the diverts have a lot to do with ground handling. Delta do not fly to BFS, so imagine the situation of emergency landing in BFS, ambulance waiting, and no one to attach stairs to the aircraft? (YES this does happen, you would be amazed!) Let alone re-fueling aircraft, new loadsheet, removal of bags, god forbid the crew go out of hours....etc etc etc
If you know you have all of these within 200nm then DUB was a good call.
Again with BA?!? Crew going out of hours, whats your best chance of making most of the delay to your passengers? Go to an airport where you or your partners do not operate to (BFS) or where you + partners have 19 daily flights to your crew base (DUB)