Why Do Most 'diets' Fail?

I have lost count with how many 'diets' I have seen out there, but are they good? I don't think so, because so many of people fail using them.
Most 'diets' out there are kind of known as 'fad diets', meaning they are pointless to be honest! To lose weight and change your body, requires a lifestyle change, not to just sign up to some diet on the internet. Many of these diets are extremely low calorie diets, which are NOT good for you, and can never EVER be sustainable. I hate companies that sell a diet that gives you 600 calories per day, because you can never do that for the rest of your life. You will go on it for a few weeks/few months, lose a bit of weight, and stop. What happens next? You go back to your normal life, cooking your own meals, shopping for food, eating out etc etc. You will gain the weight you lost, because your body has been starved for a period of time, and will cling onto the food you start eating. Also, a lot of these diets do not educate people, so once they stop, they don't know what they should be eating, how much, how to cook it properly - therefore they go back to their old ways, or back to the company and pay EVEN more money and go on a 'diet' that is not healthy.
I have said it so many times and I know I will have to say it for the rest of my career, but to get in the shape you want, you have to put effort in, and even learn a few new skills such as cooking.
Many people end up getting fed up with their 'diet' because its too strict - they can't eat any of their favorite foods or go out enjoying themselves. I am not a fan at all of diets that are 'shakes', that give a set calorie limit and you have 3-5 shakes per day. This is what I call a lazy diet, because you do nothing. So as soon as you stop it, you have no idea what to do, because all you are used to is mixing up shakes. This is what I mean by a lifestyle change, you can't just expect to drink a few shakes and your body is transformed forever.
Most diets fail because people lack the effort, but they also fail because so many of them are short term fixes, instead of long term results. Eat healthy, exercise regularly - you can do that for the rest of your life!