Brand loyalty might matter when the cost of a good is relatively low and the availability high. I can basically choose between coke or Pepsi anywhere, and they cost about the same, so why not go with my favorite?

For airlines availability with a preferred carrier is not guaranteed, and prices can vary wildly. Do I have so much brand loyalty that I will pay perhaps 2x the cost? Like most people, I wouldn't.

In terms of availability and cost, LLM providers are much closer to Coke than to an airline.