I've read that one of the reasons the Japanese were so harsh on POWs was (aside from the code & general sentiment of), they had no provision for them.
Difficult as it was, they generally failed to do for themselves, and this exacerbated the issue?
Japan was a third world country when (they?) started the war. As was mentioned before & before, they planned for a short/aggressive war that would end in favorable compromises.
The best laid plans of mice & men....