The taller you are, the larger your build can be + more mass you can carry while still having a very low body fat percentage. This is why BMI is normalized by height.
Someone who weighs 150lbs — but who is 6'8" — is actually underweight. To be that weight at that height, they'd have to have so little fat and muscle that they'd be positively scrawny-looking, and would be experiencing many of the same problems (e.g. always being cold, muscle spasms, brain fog, paresthesia from demyelination of nerves) that someone who is 5'8" and 90lbs does.
Someone who weighs 200lbs at 6'8" looks, and is, healthy; just like someone who weighs 140lbs at 5'8".
Someone who weighs 150lbs — but who is 6'8" — is actually underweight. To be that weight at that height, they'd have to have so little fat and muscle that they'd be positively scrawny-looking, and would be experiencing many of the same problems (e.g. always being cold, muscle spasms, brain fog, paresthesia from demyelination of nerves) that someone who is 5'8" and 90lbs does.
Someone who weighs 200lbs at 6'8" looks, and is, healthy; just like someone who weighs 140lbs at 5'8".