It's real choice. Even if they're all owned by the same company, the burrito place still offers burritos, the burger place still offers burgers, the pizza place still offers pizza, etc.

Offering everything at all the locations would be terrible, because you just can't cram that much into one tiny airport concession kitchen. And offering the same limited menu at all locations would also be terrible, because different people like to eat different things.

Ah, but you're assuming that the choice that matters to the consumer is "what do I want to eat?" as opposed to "how many companies operate concessions in my local airport?"

and they all serve $28 beer