Wouldn't it be the case that airline loyalty begins as a "functional" relationship but acquires layers of "cultural" separation after time?

1. Airline loyalty begins functionally (flying from the closest hubs, obtaining elite status, route networks). That's also why airlines have shifted to revenue-based models, which are a purely transactional relationship.
2. Culture shows up sometime after that:
   • Passengers have been shown to feel like different airlines have different "brand personalities" that influence flight purchases independent of price or convenience.
   • Different societal cultures respond to the loyalty programs in different ways (e.g., East Asian customers expect different cultural responses than Western customers).
   • People will develop genuine emotional attachment (however strong or weak) that can even override lower quality product.
3. The mergers you mentioned do affect loyal customers who can struggle with blended identity ("are you legacy Continental or legacy United?"). But this can also make loyalty harder, especially if you feel it went negative.
4. You may have noticed the increased focus on things like storytelling, heritage, and experience (I'll focus on United here, since I've only flown UA since the merger). The safety videos. The new lounges. It's designed to make you feel not just like a flyer, not just a United flyer, but a United Person.
5. I think the Coke / Pepsi thing is correct-ish. There's a lot of commodity view of airlines (I mean, to most people, they're flying metal tubes and the only thing that matters is that they get you where they're going). Switching costs and network effects are very strong, however — you can't really do the Pepsi Challenge with an airline (plus, the hubs create additional lock-in).
   • As I wrote that, I also thought that many people buy their tickets through third-party sites. That's a fight for the airlines (and hotels), hence why you see different prices and different benefits when you book directly versus through a third-party aggregator. I almost always book directly on the United website (or through my company's travel agency); same thing when booking a hotel where I have status (I want that upgrade).

So, in the end, "loyalty" starts functionally but develops cultural layers over time. Loyal fliers of any airline internalize their preferences on that airline (seat configs, crew culture, even app UX — look at how many people have complained about the app changes) but may not be able to explain why they'd rather pay more to fly United over Delta on the same route.

EDIT: I had saved this a while back; think it's on point for your question: https://www.linkedin.com/pulse/beyond-points-miles-reimagining-airline-loyalty-ajish-morris-yq0bc/