Considering Germany and Japan both lost the war it seems odd to me that it at least seems so imbalanced to me.
New here so I don't know what ELI5 thread you are referring to, but here's my answer(s).
While crimes committed by the Japanese were cruel and inhuman it was only the Holocaust that had as it's goal the extermination of an entire race. We learn about the Holocaust and its causes so that, hopefully, we can avoid it happening in the future.
Also, simply in terms of volume, German war crimes in WWII were an order of magnitude greater than those of Japan. The war with Germany was the cause of the vast majority of deaths in WWII.
Reporting bias. Reporters were on hand to record the liberation of the Nazi concentration camps and the conditions were graphically reported at the time. There's comparatively little solid evidence of Japanese atrocities.
Racial bias. Most victims of Japanese atrocities were Chinese.