Even outside of that it's very easy to run into a glass ceiling as a foreigner though, yeah. There's relatively few companies where you can work your way up into lead or management positions - though this is often because foreigners simply don't acquire the Korean skills they'd need to manage Koreans. There's some amount of luck and strategizing your career path involved to make it work, and that does leave you with narrow paths to the goal. Engineering and market research/business are probably the easiest fields at least.
Don't get me wrong, I'm not really blaming anyone for failing to make it work and getting out. There's a lot of wishes/desires (in choice of job, in choice of lifestyle, etc.) that are legitimately and totally incompatible with life in Korea as a foreigner, yet have nothing wrong about them.