He may have been concerned it would land him in more hot water. He might have understood he would lose anyway and getting rid of them would make the attackers look bad and he might get his country back, where if he used them, there would be no way.
WEAK!!! The US was invading his country with "shock and awe"...do you really think he cared how the "attackers" were perceived? The purpose of having WMD to to destroy massively. If he had 'em, he would have used 'em.