That does not appear to be universally true. For example, Japan has not exercised stringent quarantines (self-isolation only applies to citizens and visitors arriving or returning from certain countries), has not closed down businesses or restaurants, no nationwide lockdowns have been declared, nor has it conducted extensive virus testing (in fact, government policy does not encourage it), and children have been going to school (although Japan was one of the first countries to close schools, which it did for the entire month of March, they have since reopened) and yet it only has 6 deaths per million inhabitants compared to 4 deaths per million inhabitants in New Zealand and Australia (https://en.wikipedia.org/wiki/COVID-..._and_territory.) On April 7, the government declared a state of emergency to fight new COVID-19 infections in major population centers targetting the capital Tokyo and six other prefectures for a period of about one month. Per a news report, "The emergency gives governors the authority to call on people to stay at home and businesses to close. With no penalties for ignoring the requests in most cases, enforcement will rely more on peer pressure and respect for authority." As you can see, these are pretty informal emergency measures with no lockdown, and people continue to work, though some work from home instead of the office. Actually, most US states have been implementing much stricter measures in general than in Japan, but with far worse results. Living in Japan (though not in Tokyo), I can say that not that much has changed and life goes on pretty much uninterrupted, and it does not seem that social distancing is well maintained by people in general. At the end of March, when I was in Tokyo for a few days, the subways were still fairly crowded and not everyone wore masks. If you go to the link above, you'll notice many other countries with similar or lower deaths per inhabitants than in New Zealand and Australia, but I don't know what countermeasures they are taking, but I do think that Japan is an exception to your assertion that stringent quarantines have eradicated COVID-19, it seems other factors are also at play.

An interesting quote on Wikipedia explains why Japan's measures are not so strict: "Under the law, the Japanese government does not have the authority to enforce citywide lockdowns. Apart from individual quarantine measures, officials cannot restrict the movement of people in order to contain the virus. Consequently, compliance with government requests to restrict movements is based on "asking for public cooperation to ‘protect people’s lives’ and minimize further damage to [the economy]"https://en.wikipedia.org/wiki/COVID-...demic_in_Japan. It seems that Japanese civil liberties outstrip those of US citizens, at least as it pertains to the virus.