There aren't any other than sensible eating, but the unfortunate combination of an overabundance of food, less physical activity and a built-in one way tendency for the body to gain weight when extra food is available makes pushing diets a hugely successful business. Few people will have long term success even though most diets start out with progress. So people hop around trying different diets and mostly failing. A great business knowing you will always have lots of new customers as they move around.
Some of the diets are based on crazy assumptions. Here is some expert commentary on one.