The New York Times of July 10, 2012, Jane L. Levere, Vacancies at the Airport, reports that smaller airports — such as St. Louis, Cincinnati, and Oakland — have been experiencing a decline in airline traffic. Ditto for the Los Angeles area Ontario airport. Which is a big problem because airports rely to a large extent on landing fees paid by airlines, parking fees paid by air travelers, and concession fees, all of which decline as air traffic declines. But even so, airline terminals have to be maintained, whether used or just sitting empty. Not good.
Airlines increasingly tend to concentrate on larger hubs and are abandoning the smaller ones.