The IAG mantra is that all businesses have to target its target ROIC to justify investment in new aircraft.
BA at LGW went through a lot of pain to secure new short-haul aircraft and the BA Holidays business has been performing very well.
IAG obviously doesn't want easyJet to grow any further LGW, but it has had other options than BA.
As for LGW-OAK, how much of a loss-leader this is I don't know but I would put money on its launch being driven by decisions taken at IAG rather than BA.