Same reason hotels do it. They assume x guests or passengers will cancel or not show up. They want to fill the plane without a single empty seat. When hotels do it, they usually pay for the guest to stay somewhere comparable. They roll the dice on x not arriving and sometimes lose.
I agree it really messes with people's plans but usually the person bumped comes out way ahead. Instead of getting physical with this poor guy they should have done what K suggested, make an offer someone won't refuse who doesn't 'gotta get home', can wait for another flight and get handsomely rewarded for their patience.
yeah but being that he is a doctor and had patients to attend to the next morning - that seems like that would take precedent over wanting an employee to have a last minute ride.