That's because people here were scarred by SARS and understood pandemics, so as soon as Covid19 hit, they all bought masks and those who weren't were frowned upon. And they put huge pressure on the government to make sure that masks were available. Also, the government started to test and trace early and very effectively, meaning that the public hospitals, which are of good quality, were never overrun. Schools have been closed since Chinese New Year (early February), any large public gathering was cancelled or postponed from February (including the HK Rugby 7's, the city's biggest event), bars were closed from early March and restaurants were to operate at 50% capacity.
Result: for a city / region of 7.5 million people, there were 1,100 cases and 4 deaths - and that's in one of the most densely populated places in the world.
Extrapolating on a population of 328 million like the US, this would mean 48,000 people infected (instead of 2.1 million) and 175 deaths (instead of 116,000).
In my view, the single biggest factor was the disciplined approach of the population to wearing masks. I simply do not understand the debate around it in the US: it works.