It's surprising that a large island like Jeju is such a closed society

Jeju is currently in the middle of a massive craze with an overwhelming number of domestic and international tourists,
and the Gimpo-Jeju route is so busy it ranks number one in the world.
But after reading a series of posts,
it's surprising to see that it's a closed society, much like places such as Sinan or Miryang.
It's chilling to think that clan culture still persists there.
I once had a bad experience with a Jeju fishing village association, but
I didn't realize it was quite this extreme.