The set of bodybuilders who have enough muscle to put them into the overweight category is a tiny portion of the population. There is a larger portion of the population who has a lot of muscle and a lot of fat, but that’s still pretty small.
Any amount of muscle can slip someone into the overwight category if they are already close. For a 5-10 male, the difference between dead center normal BMI and pre-obese is 20 lbs, not a crazy amount for a casual but consistent weightlifter.
BMI 'works' because it just looks at the total population, and doest care if it doesn't fit edge cases.
Yeah, but that’s hardly the muscle at fault. If someone has 20lb of extra fat and 10lb of extra muscle, it seems a lot more honest to say the fat is why the person’s BMI is high.
To be clear, BMI is definitely a very “rough and dirty” estimate. Certainly there are healthy people with a BMI classified as overweight.
But, when considering the population rather than the individual, these outliers become insignificant.