The Iraqi motivation is harder to establish. Why, if it had no WMD program to hide, did Iraq not welcome the inspectors back with open arms and let them see whatever they asked to see, knowing they would find nothing amiss, in order to receive a clean bill of health, be free to resume oil exports and be rid of the embargo? That would have strengthened the Iraqi economy and conventional military, and would have opened a path to resuming WMD programs, once the inspectors were gone for good.
The answer is impossible to establish with confidence, unless Saddam Hussein comes clean. One possibility is that he was afraid the inspectors would stumble on something else, such as mass graves and other evidence of atrocities (which certainly were taking place). Another is sheer stubborness and a refusal to admit defeat by the inspection regime. A third is deterrence, the hope that fear of a hidden WMD program would deter the United States and its allies from a Second Gulf War.
The Iraqis succeeded in a remarkable deception: They told the truth about WMD while convincing the world that they were lying. But they misjudged the American reaction to their deception. They got inside the intelligence decision loop, but not the strategic decision loop, which took the deception as grounds for the Second Gulf War, and will probably take Saddam Hussein to the gallows.