lololol where do you see these koreans?
I think it's just the geographical reason and some genetic reason as well.
The four season was clear and the weather was so fine before the war and all that urbanization.
And Koreans have the lightest skin color. Most Koreans are pure, as u can see their last name is Kim, Park, Choi, and go on. It's like the straight bloodline. Historically Korea was invaded many times by surrounding countries but defended off and survived & maintained their culture and heritages.
As for Japan, Japanese are mixed with some Indians and nothern part & Southern part of Japan are really different.