Hardcover books do not sell as well as softcover in airport bookstores because people want portability. For the same reason, coffee table books, large books on photography and "souvenir" books are not usually fast movers, and therefore infrequently carried in these stores.
Bookstores stand between the publisher and the consumers. Your ability to deliver the "book experience" is constrained not only by the static display of your books on shelves but also by store employees' lack of knowledge of your book/topic/author.