Why does the BMI calculator say I am obese?

It says a normal weight for 5'6 should be 114-154. If I were that weight I would look like a rail! I am like 210 and I think ideally 180 would be a good weight for me because of how my body is structured. People always think I weigh less than I do anyway.
Why does the BMI calculator say I am obese?
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