Bush wasn't the only one fooled, of course, as the Congress approved the invasion as well.
And yet, the allegation that he wanted to buy yellow cake from Niger was a part of the intelligence that was used to justify the invasion.
Maybe government intelligence is really an oxymoron.
Saddam Hussain didn't believe that his ally, the US, would invade his country. He was not afraid of us (which turned out to be his undoing), but was afraid of Iran. He wanted the Iranians to believe he had WMD so that they would leave him alone.
Now, there's a good question, that could be asked along with a lot of others about this particular war. Why is it just now winding down after six years, when it was supposed to take less than six months? What happened to all of the weapons owned by the defeated Iraqi army? There is a long list of unanswered questions. Why that yellowcake wasn't shipped out of Iraq when it was discovered is just one of them.