What was the most likely reason that Allied leaders did not completely believe or understand the full ramifications of the "Final Solution" when they first heard about it?

The reason why Allied leaders did not completely believe or understand the full ramifications of the "Final Solution" when they first heard about it was that they could not believe Hitler would go along with such a horrific plan and have the support from the people. They did not think the Jews were to blame for everything, and thought that Hitler's plan was crazy.

They did not believe that someone could do something so horrible.