The problem with other diets has been multifaceted and usually falls into a few common categories.
Some diets require the dieter to do too many calculations, adding up points and calories, or weighing of food. Some people just can't do that or think it's too much work. They end up failing before they even begin.
Sometimes diets fail because the dieter reaches their goal and thinks they are okay to return to previous eating habits. They end up putting the weigh back on. You breathe every day, you eat every day, you should be on a diet every day. Diets aren't temporary. They are lifelong.
Another common reason is that the dieter can't stay on that diet. If you hate protein, you should not be on a high protein diet. You shouldn't choose a diet that is unpallatable. You should chose one that incorporates foods that you like.
Fast Fad Diet:
One common reason that a diet fails, is because it is a fad diet. Some diets claim that if you drink their juice or shakes for a month (or a few days) that you will lose a ton of weight. Or that if you take certain herbs for a short period of time, that you will lose weight. Any diet that makes claims of quick fast weight loss is a fad diet. Do not try any of these fad diets. A lot of times these are scams and or companies trying to turn a quick profit and go out of business. Or worst yet, sell you dangerous substances which can cause heart defects and heart failure.