This gets into iterated game theory: even though the value of an empty seat is basically zero at takeoff (marginal fuel and cabin crew labor don't add up to a l

This gets into iterated game theory: even though the value of an empty seat is basically zero at takeoff (marginal fuel and cabin crew labor don't add up to a lot), the airline has a long-term incentive not to reduce the price so that the market for that one flight clears, because in the future it doesn't want people waiting for cheap last-minute tickets they expect will again be available.