WOT ping.
There are two main reasons why Saddam regime chose to build the Precursors for the chemical weapons rather than the final product. The first one is that those Precursors are classified under what is called dual use materials where it can be used both in civilian and WMD industries, and Saddam regime can always claim that these precursors were produced for civilian industry. The second reason is that the Precursors have longer shelf life than the final chemical weapons program which means it can be stored for a much longer of time and assembled.