Yeah, I was very surprised when I saw how big the Korean Steemit community was. The fact that there is a trending "KR" tag. You rarely ever, and most of the time, never see a Korean community so present on international platforms. Usually it's all Naver blogs, or Apreeca TV... something really exclusive to Korea.
I think there are two distinct reasons for this though:

1- Korea's younger generation is becoming, culturally, more aware of what's going on outside of the country. They don't seem to be restricted to the Nationalism or Urinara-isms, than the generation before. You see this with other trends in social media; the steady rise of Instagram, and Facebook in Korea. The youth aren't just limiting themselves to Korean branded networks.
Most networks are dominated by English, and I think this pushes out a lot of international communities like Korea, or other countries. Yes, they study English quite extensively, but don't ever really use it, or have good English skills outside of a text/test in real world practice. However, Steemit has already cemented a place for Koreans, to share in Korean. I think that helps immensely. It allows for people to comfortably try and new platform, while also being able to roam across different cultures, and for other people to at least look at their pictures, even though they can't understand Hangul. Look at all the people in this post saying "I need to learn Korean!" That's awesome!

2- Bitcoin certainly is popular in Korea, and I think it's this tie with cryto-currency, also brings more people to Steemit in Korea. I don't think this is exclusive, as I joined Steemit through a curiosity with bitcoin.

3- I think Korea, and maybe Japan, and China; they don't appear social, or outgoing in public, amongst "strangers," but once you're in a social circle, when they're with friends etc., they REALLY open up, and come to life. I think this real world quality shows in their internet presence as well. The KR internet community is HUGE, but they all support one another, because they are in the same circle.

I'm actually really happy to see Korean culture and a Korean community on Steemit, as it allows me to interact with Koreans more, as well as share my own experiences in Korea. @ramengirl is a great example as well; sharing across three different languages, and garnering outside attention, getting people interested to branch out. It's great!

Sorry for the long winded post lol.
STEEM ON!