It all comes to what part of the curve the country is now, the choice being total lockdown incl. economic shutdown vs aggressive testing.
Considering US lapsed on aggressive measures in the beginning and that proper test kits are just being flown in from Italy[2]; total economic shutdown seems to be the only option left.
P.S. There are still high-risk countries which hasn't gone into lockdown neither doing aggressive testing as of now, claiming the number of cases are low although the day-to-day delta is increasing exponentially.
[1]Italy correspondent of Aljazeera gave this information multiple times on live, couldn't find static link to it as of writing.
[2]https://www.msn.com/en-us/news/us/air-force-flew-500000-coro...