Because Japan's currency deflated, while the US currency inflated. Printing of money is simply a means to control deflation or inflation.
All of the "thought experiments" on deflationary spirals ignore the fact that one happened: the Great Depression of 1930s. And back then, the US Monetary system was pegged to the Gold Standard.
We fixed the problem by getting off the Gold Standard. It turns out, basing your country's economy on a deflating commodity was not a good idea.