The explanation I always hear is that they don't have time to cook. To them that somehow translates into being forced to eat junk food all day at work while then grabbing the worst possible foods at mcdonalds on the way home. There's a million proper solutions to that problem, from better time management, to finding healthy foods that are easily portable, to just skipping a meal if you're hardly moving all day. But people seem to find it to be an acceptable excuse for some reason.