I suspect those 4 cities are doing more than just wearing masks. I’m having a hard time tracking down the interviews (I think it was Dr. Jim Yong Kim who said this), but there are two types of transmission between households and within households. Mask wearing, social distancing, quarantining, contact tracing, and some other measures can help to reduce between house transmission. However, you need to stop the within house transmission, too. To stop within house transmission, people are removed from their home and isolated in medical facilities in some parts of Asia.

Stopping between house and within house transmission is what I suspect those 4 cities you mentioned are doing. North America is more focused on stopping between house transmission.

Anecdotally, I know some cities in South Korea have quarantined people by placing them in an isolation room (4 people per room spread 6 feet out each wearing a mask 24/7) until they test as being COVID free. This was around 20-30 days from what I understand.

In Canada, if you quarantine, it’s 14 days in your own home. Mostly this is on the honor system. If you live in a condo / townhouse / strata or your neighbors know you’re quarantining, they can report you for violations. When quarantining, you’re restricted to a single room if you live with others, but there is still risk of passing it on to others. Anecdotally, I know of a case in Canada where an individual quarantining in their room has managed to pass COVID to 3 others who live in the house. These people were wearing masks around the house when not in their own room. If this original person was isolated in a hospital, the spread would stop at one. Since they weren’t, it ended up infecting the entire house.