Why not? Because the public perception was of a first class nuclear weapons facility ready to turn whole countries to glass. While a true threat on a serious scale, the image of old gas bombs and aging raw nuclear material from third world mines just would get laughed out of town. Better to just ignore the press and do what must be done.
And then, when you find it, you drag the reporters to the site, you toss them into a HazMat suit and you give them a tour of what you found.
It was a huge political blunder for the Bush to allow the US media to say "You lied about WMD!" without making an effective response. I still don't understand why we were silent, when we found what we were looking for.