Seriously, if you're a celeb over there and caught smoking a joint, your career is basically over.
Even the infamously prudish U.S. is more accepting of it.
I'm guessing it's a leftover of U.S, imperialism, like how all their porn is still censored.
I've heard that in past centuries (like prior to the 20th century) Koreans believed that weed had medicinal properties and they used it as part of their traditional medicine.
It makes you feel alot better real fast so it makes sense.