If you remember that BA and AA share a joint business across the Atlantic, it’s not surprising at all. There are many permutations of rerouting that are available from LAX, but very few from DXB if the subsequent BA flights are busy. QR is an option, but means revenue leakage that wouldn’t be the case with AA, and may also be full in any case. EK is no-go as they don’t have any kind of interline agreement.