There really is no such thing as "big-boned people." But the BMI is broken; average BMI is useful for looking at a population, but not an individual person. It's just dividing the height and weight, so it has no information you can't find by looking in a mirror.
Since it naively divides height and weight, it's not useful for athletes; it doesn't account for muscle mass. At 6', ~190lbs., my BMI is 25.8, which is "overweight," and is clearly wrong.