While it's absolutely true that the people who run airlines know that all sorts of problems can happen, it's even more true that they don't care enough about their paying customers to waste good money on the non-value-added resources necessary to handle the problems. They know that airline passengers have no real alternative to flying, and that their competitors care as little about their customers as they do. So their solution for dealing with the inevitable problems is to let passengers stand in line for hours at optimally-lean-staffed counters. The Security Police can deal appropriately with any passenger who displays any inappropriate lack of respectful docility when, after waiting for hours, the optimally-lean-staffed counter clerk informs him or her that the next available flight is in three days, and until then you're free to stay in a hotel and buy meals at your own expense since the airline has no liability or responsiblity for the delay-- NEXT! Airline executives know that no matter how furious a passenger may become as a result of such shabby treatment, that passenger will almost certainly be back in line in the near future to wait with resigned docility for another round.

Airlines exist exclusively to provide their shareholders with an attractive return on their investment, and particularly to provide their top executives with millions of dollars of well-deserved annual bonuses. That is best accomplished by running a lean, efficient operation in which every airplane is fully packed on every flight. Any margin for the inevitable glitches is best fully borne by the passengers, since any money wasted on unused capacity for handling surge or error conditions is money stolen from the pockets of executives and shareholders.