The issue was both frequency and activity. Anyone who's been to a Korean gym will tell you two things: they're widely empty and those that do go usually just end up slowly walking on a treadmill (slowly, so they can watch their favourite TV drama on the screen). In other words, even those that work out don't really "work out" (with few exceptions, of course...there are Korean bodybuilders and runners and such). Most people don't even do that, and many work sedentary jobs and finish work by going home or to an internet cafe and being sedentary. This is based on job, of course; I don't think I've seen fat cops but I have unfortunately seen fatty fat soldiers.  Food is a lot easier to come by lately, and the culture highly encourages lots and lots of eating. While Koreans will tell you you're fat, they're also incredibly shocked when you eat less at a meal. Imagine that: they tell you to your face that you're fat and need to stop eating so much, and then they have no idea why you eat less at meals. This isn't everyone, of course, but holy shit it happens often.