Why would the CIA want to more or less dis-prove the purchase of Yellow cake from Niger??? that's what I want to know.
My opinion is that the French have an obvious interest in discrediting any stories about Niger uranium smuggling. Beyond that, France was directly in bed with Saddam, supplying him with weapons right up to the beginning of the war. They had oil contracts with Iraq worth maybe $100 billion, that would be worthless if Saddam left power, and they were large recipients of Oil For Food bribe money.
They had every interest in avoiding this war.
CIA's interest was in de-fanging this president. Why, is less obvious. It could be strictly partisan, or it could be something more.
Ex-CIA Baer, in his book, mentions that former CIA quite regularly are hired by the Saudis as "security consultants". I believe that the Saudis have considerable influence at CIA. Wilson was in bed with a Saudi investor, and a Saudi-funded think-tank.
There is a long list of State Department people who, after serving in Saudi Arabia, retire to establish their own "institute".
So through their friends at both CIA and State, if the Saudis oppose some element of American policy, they have tools to modify and influence it. Bush Senior has business connections with the Saudis, as we know, and he seems to have opposed the war in Iraq along with other members of his investment firm. W Bush, on the other hand, went ahead with his plans and has had no end of games run against him from both State and CIA.
Wilson was apparently neutral or even pro-Bush in his public statements until he joined the Kerry Campaign, which corresponds to when he wrote his op-ed piece. So this is to me an important detail. It could be strictly partisan, Saudi influenced, French/Iraq influenced, or all of the above. Take your pick.