Her approval rating was 4%. Obama didn’t gin up any protests. South Koreans just hate her. They are saying that the outgoing UN Secretary-General will run to replace her.
I know she was unpopular. I have heard rumors about the admin’s involvement in the protests. And the admin has screwed with other elections: UK, Israel, Italy, and Spain spring to mind. Plus the timing of the impeachment, right before Obama leaves and Trump takes office, also makes this suspect.