Because they can’t. Culturally, they can’t. Losing to a mixed race bunch of round eyes destroyed much of what they hold dear.
I worked with a Japanese national for a while. He had very little knowledge of WWII, other than the Americans nuked the Home Islands and how horrible it was. Of course, there was an old vet who, gently, gave him an education.
By the end, he feared he could never go back to Japan. He had changed so much he was not the same anymore.
I have Japanese friends and acquiantances. They know what happened and some will talk about it. They also are quite humorous about their own culture (not related to war). Of course, with the exception of one, they live in NYC. Only one returns to Tokyo every year for months at a time. She’s a little uptight. I had a friend who had a fashion company called ‘Nips.’ This was in the un-PC 80s.
When I lived there in the late 80's, the most popular book was a rewrite of WWII into a glorious Japanese victory. It was hugely popular and was indicative of the culture's refusal to admit to their role in the destruction of WWII. Most of the Japanese I met and became friends with knew nothing of Japan's actions in the war and why that caused Hiroshima and Nagasaki. There were several times we went out to dinner and would have to leave the restaurant because someone (usually an elder) was cursing me out for using nuclear weapons on their country.