It's just that TOO MANY calories are bad. Everyone likes eating food, but most people don't want to get too many calories, so low-calorie foods are helpful. I've lost a lot of weight by limiting my daily calories to around 16-1700, and that's involved finding plenty of low-calorie snacks to make sure I don't go hungry but I don't go over my limit either.
Calories are, of course, vital for energy, growth, and for life. You need at least 1200 a day just to keep your vital organs going!