That's because such extreme measures are not necessary. And mark my words, they are permanent just like the Patriot Act and other grossly unconstitutional responses have been to crises.
Could be. But we have an example where a country was able to control the spread without quarantining healthy people (South Korea). To quarantine healthy people is to dismiss 4 or 5 centuries of medical practices which were employed during every major pandemic and epidemic plague we've dealt with and which were deemed most effective. We've said in this case, that the past century's well-informed practices are no longer effective. Total nonsense and it is and has caused more catastrophic effects than the disease.
True in that several Asian countries, so far, (such as South Korea, Singapore, Taiwan) have dealt with this crisis far better than the USA or most European countries.
But false in claiming healthy people were not quarantined.
These countries treated Corvid19 extremely seriously, and took draconian actions. Actions that would unlikely be accepted in the USA (or UK). And they started as soon as they suffered the first reported case. They did not even wait for a few deaths. They did not dismiss this new virus by saying 'but thousands of people die from the flu, so by comparison this is insignificant".
Anyone who tested positive had to quarantine (and in Singapore, that meant being admitted to hospital - the authorities did not trust people to quarantine at home).
Further, they aggressively contact traced all people who had any significant contact with the infected person. These contacts were ordered to quarantine at home for 14 days (i.e. forbidden to leave their home).
Example of how Singapore dealt with the 'crisis' (one of the first countries outside China to get cases of Corvid19):
How Singapore stayed one step ahead of the virus
Quarantining in Taiwan:
Coronavirus: When the police knock at your door
Unfortunately, it is now far too late for Western countries to take the kind of actions that South Korea and Singapore did (and still do). The horse has already bolted from the stable. All we can now do is to attempt to slow the spread of the virus so that the hospitals are not overloaded.
It is far too late to start contact tracing. In the USA there were about 33 thousand new recorded cases on 7 April. With 30 - 40 significant contacts per person, that would require tracking down over 1 million people, and ordering then into quarantine for the next 14 days! And again the next day. Impossible.
The UK should have acted sooner. The longer you leave it, the more difficult it becomes - and less effective. But hindsight is wonderful.