True but moreso than your average business, airlines are dependent on the revenues from the customers at the margins. In the short term, the plane needs to fly whether it's full or not. Even the lowest fare customer brings in more revenues than the added costs of flying them. It's the fixed costs that need to be spread across a plane full of passengers in order to make it all profitable.

An airline like Delta will adjust but there will be pain for them in the short term and pain for customers in the medium and long term with fewer, more expensive flights. All of this assumes these changes actually lead to customers changing their behavior rather than simply saying they will.