They still have to offer replacement flights, and if the replacement flight isn't reasonable they have to refund. They can't just keep your money.

Don't forget that a lot of flights are business flights. Fortune 500 companies will negotiate deals with the airlines, and they will ensure that getting there matters. Sure the CEO flys the company jet, but the next level down rarely does, but they talk to the CEO and will ensure that the chosen airline will get their people there by contract (wherever there is), if the airlines start failing to get people there on time these contracts will change since the large companies have enough money to matter. Those who fly a lot (again likely for business, even small businesses sometimes have someone flying several times a week) again are people the airlines need to make happy as they will go to different airline if there are problems.

Which is to say they can screw the "common man" who rarely flies, but most of the business is people who have enough power to to to airlines that treat them well and at that point it normally isn't worth screwing anyone.