Except it doesn't do any such thing, as I explained in the post you quoted. It makes zero distinction among all the different things that contribute to BMI and therefore it isn't useful except in the context if individuals and their specific factors.
As I also explained, the lifespan of Japanese people, fat and thin alike, is not dependent upon BMI except in truly obese sedentary people just like everywhere else in the world (and such people hardly need a BMI measure to be identified). That's because an overweight person who is very active and physically fit doesn't usually experience any of the common consequences of obesity. Consider sumo wrestlers for example; they're huge and really fat, but as long as they are training and competing, but begin to develop those kinds of problems when they stop competing because they generally maintain the same high consumption diet. After a career of deliberately getting as large as you can it much be awfully hard to change your diet but for the average person, the main thing is just to be as physically active as possible and you won't really have to worry about your weight although sufficient nutrition is necessary, obviously.
Thanks for playing.
Please try again when you grow up a little.