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.

I learned this when I was in the military and going to medical to get a checkup.

I’m a 5’5 male and I weighed about 160 lbs at the time with a pretty strict workout routine which consisted of weight lifting and cardio 4-5 times a week.

The corpsman that was taking my measurements and weight told me I was obese after recording my BMI, and I was shocked, but he told me not to put any thought into it.