They basically did a speedrun of modernity. After the Korean war, they industrialized, moved most of the population to the capital and began to immediately adopt whatever the western elites were into like feminism, satanism, living in a pod, antinatalism, etc.

At this point, it's the country with the lowest Total Fertility Rate, the "developed" country with the highest suicide rate, the country with the craziest feminists.

South Korea is like an experiment jammed into a hyperbolic time chamber.