> So what is keeping the average Japanese of today ignorant of their recent history?

Presumably some of the same things that keep the average American ignorant.

Top of the list: reliance on schoolbooks dumbed down and smoothed out for fourteen-year-olds, and lack of interest in pursuing the subject further.

One difference between the US and Japan is that Japanese schoolbooks have to be approved by the central government. Do Japanese college courses endorse the schoolbook version of history?

In fact, the U.S. oil embargo really did lead Japan to attack Pearl Harbor. Japanese oil reserves were quickly drying up owing to the unprovoked war against China that the U.S. was trying to stop.
(Number of Chinese civilians slaughtered in Nanking: well over 100,000 - comparable to the death toll at Hiroshima.)

Many Japanese officials knew it would be almost impossible to beat the United States, but they decided to risk it rather than be humiliated give up the dream of ruling East Asia and the Pacific. It was all or nothing. If they lost, at least they could go down fighting rather than be dictated to by an inferior race.

Lesson from Munich: never try to appease an aggressor.

Lesson from Pearl Harbor: never tighten the screws on an aggressor.

The average citizen of any nation doesn't want objective history anyway. It's too confusing and not very inspiring; but feel-good history always makes you feel good.