Because foreign pilots' standard is much to be desired, way below the local Koreans superior flying skills.
Trust me, that's actually true, they are really absolutely the best pilots amongst the lot.
Well, at least that's what I gathered through my mates there; who seemed to think that you gotta be mad to give it a go when you have any other reasonable options.
Caboclo
All the statements are true apparently. The one glance pay check comparison between locals and foreigners, the latter are paid more. The locals did get their living index increment plus bonus, the foreigners didn't.
Bear in mind though, they have not violated any of the contracts, again that's what I was told.