> why not do it now?

I'm guessing to give people time to alter their plans etc.

> Unless they are magically different from every other country

They seem to be! Nobody really knows why, but even if their testing is inadequate you'd still expect to be seeing a lot more deaths if the virus was rapidly spreading. More info: https://www.japantimes.co.jp/news/2020/03/20/national/corona...