To respond to the original question: because BA offers a reasonable service at a reasonable price. I have only once had an issue with misrouted luggage (well before fully computerised baggage systems) and I have otherwise only ever experienced entirely satisfactory on the ground and in the air service. There is also one other consideration: some years ago I stupidly ate off a street vendors stall in Egypt (Doh!!) and, with (what I subsequently learnt) was a dose of shigella dysenteriae, I got to see two sets of sights from Luxor northwards to Cairo. Whereas my ticket was not a flexible one, BA bent over backwards to enable me to get on a plane back home fast. If anyone here is in need of a crash diet, try dysentery – you can pretty much see the weight falling off, or is it “out” of you? That act bought a lot of customer loyalty here. It is also the case that BA C/C do not go in for the fawning obsequiousness that some on BT seem to like but I personally loath.
Beyond that, as SimonS1 has pointed out, most carriers (this is even more true of the LCCs than the legacy carriers) do not have their own ground staff any more and rely instead upon ground handling companies because the number of flights does not justify having their own stand-alone ground operation. The interoperability and liaison with these third parties is nowhere near as close as with their own ground handling operations and, frankly, many agency ground handlers give every impression, in my experience, of being almost completely indifferent: your airline is not their direct employer, so why bother?
Canucklad: how many airports on the continent allow competing ground handling agents? As often as not, it’s an airport operator monopoly. A reflection of the fact that a single European market in services remains incomplete.
We also experienced the longest ever wait for baggage at BLQ; it must have been lunchtime.