Korea (and the other countries mentioned) reacted hard and strongly at the start of the pandemic, and kept numbers low.

In Korea the worst day had just over 1000 new cases in the whole country. They had forced quarantine for those infected and very strong (legally enforced) contract tracing[1].

Meanwhile in the US and Europe they seem to have abandoned contact tracing completely (unsurprising given how widely spread it is now). Lockdown (or vaccine) seems the only alternative in that case (or lots of deaths of course).

[1] https://en.wikipedia.org/wiki/COVID-19_pandemic_in_South_Kor...