Japan and Germany, like the rest of Europe and the United States have mixed economies.

Is your question why the United States holds more true to the idea of "classical liberalism"? It's because since Lyndon Johnson the United States has seen a backlash against anything that could be perceived as "leftist". The Democratic Party has shifted very far to the right politically and especially economically. This is both from a fear of communism and the fact that the country has truthfully never wavered from it's classical liberal origins, whereas other European countries have embraced socialism or "planned" economies.