Why don't K-pop idols look underweight?

K-pop idols are known for extreme dieting/exercise, and many are listed as having underweight BMIs, but they don't look excessively skinny. They don't have a lot of muscle and they always look soft. They don't seem to have super-low body fat.

If you think of any western celebrity who is called out for being "too thin," they're extremely sinewy, bony, and gaunt-looking. Why don't K-pop idols ever look that way? I'm honestly confused about why people complain about idols being too thin, because they just look like normal-slim people who don't work out.