Food spoilage can upset many a person. You may have seen restaurants resisting giving out doggy bags. They have no control over food handling and storage. It only takes a matter of hours for some food bugs to multiply to dangerous levels. Food must be kept above or below certain temperatures to minimise the multiplication of bugs (that's the technical term for bacteria). Once its out of the fridge or out of the oven, it goes off fast. Many in the food industry suspect that food poisoning is very prevalent in the community - often regarded as a tummy bug or bad hangover. Realistically, its probably that 2 week old pizza that hung around on the bench overnight before going in the fridge (or whatever).

Its cheaper for airlines to dump unused food than fight with the coroner in court.