>>How much easier than "eat less calories than you use" can it be?
Because we have no way to accurately measure how many calories your body actually uses. We only have very, very rough estimates and guidelines, and even then there are so many factors to take into account (some personal, some environmental) that it will simply overwhelm a beginner. For example, when you are at a caloric deficit, your metabolism slows down and therefore burns fewer calories too. Not only that, but your hormone balance changes too, and your body can re-prioritize which tissues to retain and which to get rid of. This is why people who lose weight don't lose just fat but also a lot of muscle, and become weaker as a result.
This is why an "eat this, not that" approach works a lot better than an "eat less calories than you use" approach. The former is very clear and tangible. The other uses a lot of rough measurements and guesswork and the side effects of its results are not always ideal.
Because we have no way to accurately measure how many calories your body actually uses. We only have very, very rough estimates and guidelines, and even then there are so many factors to take into account (some personal, some environmental) that it will simply overwhelm a beginner. For example, when you are at a caloric deficit, your metabolism slows down and therefore burns fewer calories too. Not only that, but your hormone balance changes too, and your body can re-prioritize which tissues to retain and which to get rid of. This is why people who lose weight don't lose just fat but also a lot of muscle, and become weaker as a result.
This is why an "eat this, not that" approach works a lot better than an "eat less calories than you use" approach. The former is very clear and tangible. The other uses a lot of rough measurements and guesswork and the side effects of its results are not always ideal.