They have pilots needing to make other flights that could delay hundreds of other people.. Sometimes mechanics are randomly needed. Happens a good bit. They can't drive bc of unions and there were no other airline flights til the next day. So they were stuck. As everyone said the bidding simply has to continue. They sell double booked seats all the time bc of no shows. It's a shit business model made legal by corporate America. But hey it's in your contract that they can legally fuck you. So that's that.