Keto is not a magic bullet or a fad diet. It is a DIET. And when I say DIET, I mean the first Oxford Definition of the word.
Diet - noun /ˈdīət/ - the kinds of food that a person, animal, or community habitually eats. - Oxford Dictionary
Why most diets don't work: Your body doesn't keep track of calories. Simply eating less calories than you burn doesn't work. In fact a calorie deficit will slow the metabolism and cause more problems. It's hormones that tell the body to store or burn fat, especially the hormones Insulin and Cortisol. Every time you spike your insulin levels with sugary foods, you're telling your body to store fat. Every time you allow yourself to become overly stressed, you're telling your body to store fat. If you already have a slow metabolism, here's a video on how to repair it: https://youtu.be/dt1DOJXAXFg
Why keto works: Keto reduces insulin spikes by eliminating all sugars and most carbohydrates from the diet. The reduced insulin levels allow your body to access energy from its own fat stores. Keto recognizes that the research linking fat to heart disease is wrong, and fat is actually a healthy and necessary part of the human diet (see Dr. Fung's works for the science to back this up.)