Perhaps its a feeling of comfort, a bit like an old blanket or a toy that one sucks at night (when was child of course) or a comfy pair of slippers! For me its the product and I am happy , in the main, with what I get. There is also the loyalty rewards which is easy to understand and easy to use (most of the time). Certainly my wife and I would probably not have had so many holidays further a field as we have had it not been for BAmiles and 2 for 1 amex vouchers.
From my wife’s perspective, she just does not want to go on airlines run by foreign companies. The suggestion of going to say Spain with Iberia is met with a frown. I did manage to get her on Qantas and Air New Zealand and they are now “fit for purpose”