I noticed that also. I think one of the reasons is due to their alliances. I fly a lot into/out of Korea and almost always choose OZ over KE mainly for the reason that OZ is a member of Star Alliance. With the exception of a handful of DL flights I took many years ago, KE is the only member of SkyTeam I ever fly and even then it's very rare. I have no real desire to be an elite SkyTeam member. I'd much rather bank my miles with *A if possible or OW as a second choice.

My guess is that most FTers are similar to me in that they prefer *A or OW over ST. So they only fly KE if it's their last choice, or if it's their own dime and they need to fly as cheap as possible. KE's much larger size compared to OZ is due a lot to Korean travelers, not foreigners. If you compared the number of foreigners on KE vs. OZ, then I doubt you'd see as much of a difference. Foreigners prefer OZ due to it being a member of *A. Koreans don't care so much about the alliances and choose KE simply because it's the biggest in Korea and has flights to most places they want to travel to.