However, in fact, it is easy to have BMI under control if you live in a moderate climate and in a city that encourages walking.
BMI is too simple a metric to have any meaning. Look at athletes, they are arguably in better health than many people, but because they have more muscle and less fat, their BMI is actually higher. Bodybuilders, powerlifters and strength athletes have high BMI.
BMI is essentially height and weight. Weight is not the same as body fat percentage. You can be underweight but have so much fat for your height that you are unhealthy and your BMI is low. You can be extremely ripped (which may or may not be healthy long term) but your BMI will be very high.