I'm going to say the switch has more to do with the codeshare with KE than cost savings.

I think the real question is why KE has a terrible lounge at their hub.

It looks like the only oneworld operated lounge is the CX lounge, which seems to be open almost all day. http://www.oneworld.com/ffp/lounge-a...ungeaccess/ICN

Is this the lounge in question? http://onemileatatime.boardingarea.c...n-airport-icn/