The easiest diet is a diet filled with starchy vegetables and fruits. It fills you up insanely, it's low on calories, and is extremely hard to overconsume.
Try eating a cup of beans, try eating two cups of beans. Practically impossible to do at one sitting. Try eating 10 bananas, extremely hard to do all at once.
People just don't realize how much calorically dense foods they eat and how little their physical activity is.