Perhaps because if he did, the penny would drop, light bulbs would go off over peoples' heads, folks would be slapping their foreheads saying "D'oh," and so on and so forth.
The argument for ambiguity is getting weaker and weaker. It used to be that one could say that if everything were fully acknowledged, the public would force the U.S. into a dangerously premature war with Iraq. Now, however, the war is on.
So, what would happen at this stage if the ambiguities were resolved? I don't think it would drive public opinion to take a stance on specific military questions, such as an invasion of Baghdad. At this point, is it only about protecting the stock market? (I wouldn't minimize the importance of the stock market, but still....)