It wasn't really a failure of the intelligence community it was a failure of the Bush administration. Bush couldn't believe his "friends" in Saudi Arabia would do anything to harm his administration, after all his family had had a long and profitable association with them for years.
Plus, at the time the Bush administration was up to its neck in scandals (anyone remember the Enron Scandal?). Bush's popularity had cratered and it was looking increasingly like he would loose the midterms and Presidential elections.