I guess they figured they had ridden that horse as far as they could, unless they came up with a smoking gun, and they never really did.
Saddam had a lot of known chemical weapons and capability that have never been accounted for, for sure. However I am a lot more skeptical about the bio weapons and nuclear programs Colin Powell was so hot about, there was almost no hard evidence on either one of a current, serious program. My personal opinion is that Saddam thought he had those programs going, and was giving a lot of black money to one or more of his lieutenants to run them, but half or more of the operating cash went into personal Swiss and Lebanese bank accounts while they gave Saddam glowing reports of their progress.