A quick spot of armchair psychology - I reckon a large part of it will be down to how captive soldiers were treated.It’s interesting how a lot of WW2 veterans have absolute lifelong hatred for the Japanese but managed to quickly reconcile with the Germans.
Were they really that much worse than the Nazis?
If you were fighting in Western Europe and taken prisoner by the Germans, unless you were SOE or a commando, chances are you would be taken to a POW camp and treated reasonably. At least paying lip service to the Geneva Conventions. Try to escape and the chances were reasonable you'd be transferred to another camp.
Get captured in the Far East and you're in for a lifetime of brutal starvation, beatings and forced labour, if you aren't shot or used for sword practice right away.
All of which probably makes it easier for POWs to view the Germans as soldiers like themselves. People doing a job and treating their prisoners as they would like to be treated if the roles were reversed. Auschwitz, Treblinka, Bergen-Belsen etc. can be blamed on the Nazis in charge, not the everyday soldiers. On the other hand, if every Japanese soldier that you encounter is a sadistic bastard it would likely be quite easy to view the entire race as evil scum.