Because people are lazy, and being told “you just have to work hard, do 4-12 sets a week close to failure, and eat in a calorie deficit” doesn’t sit with them because people want shortcuts to fitness. Because of people wanting shortcuts, there will always be a market for shortcuts, and it doesn’t matter how bullshit those shortcuts are, people would rather follow the bullshit than accept that it’s not that complicated and they’ll just have to work hard.