To answer this simply, there are two points to be made.
That the Japanese forces fought with such tenacity and emotion that the U.S. was afraid of having to fight an insurgent trained under their control of the island.
Japan's defense would be handled by the United States Armed Forces rather than by their own, now weakened army.
And I'm left with some confusion, presumably you mean Germany as in post World War 2, in which case their, arguably, was no Germany after that. It was divided into zones and controls by the Allies and the USSR.
If you mean Germany in World War I, that it's because Germany still had to handle it's own defenses, unlike Japan after WWII.