Last week my return flight from Denver was delayed by 6 hours. If it had been cancelled I'd have had to fly to Chicago, get a hotel, and look for a flight to MSP the next day. There were no seats from Denver to MSP for over a day.
This is now the rule. Underpaid junior analysts attempt to quantify the chaotic and airlines have increased overbook rates. I suspect academic mathematicians will ultimately show that the system is non-linear, and that the consequences of overbooking cannot be predicted within reasonable bounds.
Eventually a few people will die from the stress of travel, there will be litigation, and the airlines will reform.
Air travel is now for the strong alone. I do not encourage my elderly parents to fly.