"Are these airports?"
Because this is not talking about "these airports" -- those two words together are not in the same noun phrase.
You could think of this sentence as "Are these, airports?" or perhaps "What about these? Are they airports?" -- the "these" stands by itself, meaning something like "these things". So it's just "ezek".
And then the "repülőtérek" comes after the subject and is the predicate, "(are) airports".
If you had written "Ezek a repülőtérek?", then ezek a repülőtérek would have belonged together as a noun phrase, and it would have been just "These airports?" -- without the meaning of "are" in it. It wouldn't be a complete sentence.