The real question is why Bush didn’t let it be known what was actually found in Iraq. At the time I recall reading about buried stories about some mustard gas, but not the nerve agent.
On the yellow cake he didn't want it to be known because they needed to get it out. They needed a secret route to do that and if every Tom, Dick and Harry knew about it they'd try to thwart the transport.
As I understand it the material was near Iran so Iran would definitely have wanted to get at it.