Well, to be fair, whether that would actually work isn't as cut and dry as one might think. One, it's really not feasible. People still have to go out and get food/necessities. Infrastructure still has to be maintained to some degree. Hospitals and associated systems need to function to not only handle the epidemic, but also other urgent or emergency medical issues that occur every day. Not to mention police, fire and other emergency responders. A month long complete lockdown will never happen here, or anywhere, really.
Even if we did, we can't isolate ourselves from the rest of the world. Inevitably, sick or asymptomatic people will come into the country, and potentially we'd have to start all over again. The point has been made that we're not necessarily trying to take cases to zero, but rather keep the peak of the curve at or below hospitalization capacity. We've been able to do that pretty much everywhere except the most hard hit areas.