major obstacles to doing this:

(1) The nature of the virus - specifically, the fact that this coronavirus is extremely contagious yet many infected people have no symptoms, especially in the first few days of infection. So they can spread it to many, many other people without knowing. Which leads to the second point....

(2) Lack of accurate testing - if you are mad about anything related to this pandemic, it should probably be the terrible lack of preparation in the U.S. when we knew this thing was definitely coming our way. The biggest problem is just lack of actual tests. If we could test everyone, then yes, theoretically we could quarantine the infected people, and the high-risk individuals, and everyone else go back to work (cautiously and thoughtfully). Another related problem is the fact that some of the tests appear to have a relatively high false negative rate, which is absolutely horrifying, because people who are actually infected are told they are not, which leads to the problem noted above in point #1 about spreading it around without knowing.

(3) Lastly, it's really difficult to completely quarantine the high-risk population. If your old parents or grandparents are healthy and completely self-supporting, then that is fine for them. I think everyone who keeps hollering about "Just quarantine the old people!!!" are imaging this scenario in their heads. But the reality is that many of the high-risk people (really old, immune compromised, or medically complicated patients) need a lot of care from people who would not be quarantined. Healthcare workers are in fact just regular people like everyone else, and so a limited quarantine would risk them infecting the people who would be under strict quarantine, despite the best efforts at using protective equipment.

Hopefully this was helpful in understanding a bit?