I have no idea as I do not know those cultures. There are many possible explanations.

However, there are not going to be factors specific to some countries. As it is so widespread its most likely its a common factor or factors. The underlying reasons are probably not that different from those in South Korea.

"By the time a child turns ten, their mother will have seen her earnings fall by an average of 66 percent, considerably higher than the earnings penalty in countries including the US (31 percent), UK (44 percent), and Sweden (32 percent)"

So Sweden is not as bad as SK, but slightly worse than the US on that particular economic factor.

"But South Korea is even worse. Almost 80 percent of children attend a hagwon, a type of private cram school operating in the evenings and on weekends"

I think that sort of thing is a factor too, and, again, in many countries.