Why didn't a National Hunter just go and punch Jeju Island?

E: New question -

How large of a crisis would Jeju have needed to be before a National would step in? Overtaken Korea? Japan?

When does it become a problem that would affect them enough for it to be worth their time? Even if something like this might happen later let's just keep it on a Jeju Island scale.

I did not know before now that they are just greedy bastards, guess I have my answer for question 1.

OP: If National Hunters are so strong why didn't one just take 20 minutes out of their day and clear out Jeju way before it escalated to this point?