I visit family in other states and I get comments like “I can’t believe you are so thin.” For context I am a healthy weight and I eat what I consider a reasonable diet. I sit and smile while I watch them drink soda and eat pure sugar and salt. I don’t care about your life choices but don’t act surprised by someone that’s a normal weight.
BMI “works” for populations. It was originally designed and characterized to measure populations, and so it’s the perfect thing to compare massive populations, like states. The majority of people are adequately characterized by BMI, just as they are by waist circumference measures. The “outliers” are vastly more likely to pipe up online.
The people who don’t understand what you mean but are obese are more likely to pipe up online.