It's been argued that basically Japan is still very honor based and when you give your word you make good on it. The generation change was essentially saying "you know how we said we had truth all those years, well we didn't and we lied to you." This was a great dishonor and the Japanese didn't want to be associated with an organization who was dishonorable.

That could be the reason, or it might be something else. Anyone else have a theory?