Why do most foreigners living in Korea have mostly foreign friends?

I was recently asked this question by Matt Kelly on Kbs world radio and didn't have time to finish answering

1. Common interests
Let's face it, to most westerners especially young male Koreans are not cool-in fact they're stereotypical nerds. Studying like machines, playing videogames, and watching soccer? Boring!

2. Language barrier
Most young foreigners in Korea teach English thirty or forty hours per week for a living, how about teaching for free in your spare time? No thanks!

3. Sense of humor
Or lack there of, from a western perspective at least. Koreans predominantly like comedy of he slapstick variety. It's not just a coincidence or trend, I believe there to e cultural and sociological roots. In postmodern (developed countries-by that I mean socially as well as economically), people have more time to reflect on lifes bigger questions. These relate mostly to existentialism, and the answers we've come to are influenced by individualism. In short, we realize that life is absurdly pointless and it's funny to poke fun at the fact (dark humor), Koreans don't get it yet, they will, just wait!