Why would they care about a court ruling in a foreign country that doesn't affect them?
Exactly, no government really cares about the Nuremberg rulings, it is not their government that made it.
Japan had nothing to do with the Holocaust
They have their own version of the Holocaust which they have no shame for. It is to Japan's convenience that if they show recognition for this totally stupid thing(Holocaust), they have no shame for their emperor's imperialism.
How?
When Stalin and Hitler were arguing about who should rule Poland, the UK could have asserted that Poland remain its own territory. That would have stopped the war. They also could have interjected against Stalin, in regards to the Ukrainian genocide.
Instead the UK sided with Stalin, but that was not in defense of Poland, as after the war, Poland became a subject of Stalin with no one defending her.