The White House doesn't think that Iraq is being honest. Why do people develop weapons? For two reasons; Offense and Defense. If Iraq has weapons, that means they are preparing to either attack another country or to defend their own. Nations attack other countries for one reason; to expand their resources. There is NO other reason for sending troops across a border. Oh, sorry. There is one other reason. "The voice(s) of God told me that they were bad people."
The Bush administration wants to do one thing. It wants to make sure that whatever WMD Iraq have does not enter the US or are used against US interests and people outside the US. Oh, and there's oil in them thar hills, but that shouldn't really mean much, should it?