I lived in South Korea 2019-2021. On top of what you said above, they have a very good very intense contact tracing system, in SK the phone/bank/government are pretty inter-connected, it's not difficult for the government to literally hunt down cluster infections and force people into quarantine, and they did. They sent out over sms the exact times and locations of places people who had covid visited, etc, etc. I think contact tracing, Koreans taking it very seriously, wearing masks correctly, actually social distancing kept things under control. Koreans a very good at following instructions when they decide to, and they do it diligently.