In Japanese culture, you must save face. No one admits a problem to a superior, either in government or business. If he did, he would lose face. Or the superior would receive the information but would not admit to anyone else that a mistake was made. I am not saying poor accounting is not to blame, but something more basic is behind it.
Now, Japan must lose face as a country to correct this problem. The Japanese will find this hard to do. Those who believe this archaic phenomenon is no longer important are fooling themselves.