The reinstated flights are empty, indeed. But that's because pax have changed their travel plans or have been booked onto a different flight within the disrupted period. I have Fico access and have seen many full flights for the last couple of days. I think BA have decided to re-instate some more flights for one reason: If certain flights are getting cancelled too often, the airline could risk loosing the departure slots. And such a slot at LHR is worth millions.