It was never meant to be used for individuals. It was designed for populations.
There are some short fat people with 0 muscle mass, and they have “healthy BMI” despite being built like a beach ball and there are tall muscular people who will never get a “healthy” BMI due to muscle and bone density from all that exercise.
For a population they cancel out and still give an accurate enough reading for the population.
But for individuals it gives false results.
That’s why the military will check BMI first, then if you fail they use a (relatively) more accurate method and use those results instead.