Actually, that is a popular misconception. Airlines have been highly profitable for the past few years. It is directly related to the degraded consumer experience. More capacity discipline and new ancillary fees have really boosted margins. Also, the cost of fuel has plummeted.
United's average quarterly profit margin over the last 5 years is 4.37%.They've dipped into quarterly losses three times during that period. They're not "highly profitable"--they're just not losing money for once.