And another reason are hot dogs.
Seriosly, open any airline web site, and take a look at the ticket price to any destination from Seatle, time it takes to travel vs. costs for the same trip from Chicago.
Take even 40% out for corporate discounts. Take a look at the savings, and then multiply it with a number of Corporate sector employees that in your opinion would travel on monthly bases.
Any business has to continuosly work on rationalising its operations, and constantly improve its bottom line. That means both income and expenses.