Airlines have had trouble with this for a long time. "The Sporty Game", by John Newhouse (1982) tells this story from the aircraft builder perspective. Over the history of airlines, the industry was a net financial lose. As of 1982, the only aircraft product lines to make money were the Boeing 727 (because so many were made) and the 747 (because it was so big).

The US used to have a highly regulated airline industry. The Civil Aeronautics Board decided who could fly where. Then came airline deregulation. Suddenly there were lots of new airlines, most of which went bust. Now we have fewer airlines than before deregulation, worse service, and constantly changing fares. On the aircraft side, airlines are buying new copies of the antiquated Boeing 737, because it's cheap. The B-757 and B-767 are being phased out in favor of the old, narrow 737.