I'm not sure exactly what's to dig at here. I don't know if I would call it a cultural obsession to be concerned with your weight. It's certainly a better habit than the Anglosphere's obsession with weighing 150kg.
It's not an obsession to "just" worry about your weight.
In Japan however it's at a point where you might struggle to find reliable records of weights because practically everyone cites their weight as much less than it is. (Allegedly. I'm no authority on the topic so take my words with a grain of salt.)
Which isn't a thing in the west.
In particular fictional characters and IRL idols are often claimed to be impossibly light because weighing almost nothing is the desirable ideal.