We're telling passengers that the flight is canceled because of a mechanical problem, but what we really should be saying is that their plane is needed elsewhere. Try this on a day when the weather is quiet and there are few passengers in the terminal. Saturdays and Sundays are best. On a layover in Dallas last week, with the weather clear as a bell, I saw a whole column of cancellations. Unless there's a saboteur at work at DFW, I figured this was prime example of airline cancellation greed.
Charters are the worst, mostly because they only operate a limited number of aircraft.
Not every airline pulls this stuff. Last year, after one of its flights from New York to London broke down, British Airways offered to re-book the stranded passengers. Only one traveler, who happened to be related to a flight attendant, refused to go. He wasn't in any hurry, he said, and would gladly take the flight once it was fixed. He ended up being the lone passenger on the Boeing 747.