The reason Korean Air and Asiana do not hire foreign F/Os is due to the country's labor law. I believe Singapore Air is the same way now. Also, as for instructing in Jeju, it sucks. Two of my buddies went in as instructors on a three-year contract with a guranteed seat on the 744 after the tenure of the contract. But the management "nullified" the contract somehow during their time in Jeju. They both quit after that.