A simple one word answer: Lawyers.
"The administration does not want the victims of Sept. 11 interfering with its foreign policy," says Peter M. Leitner, director of the Washington Center for Peace and Justice (WCPJ). Leitner says the Bush administration may be concerned that if other victims of the Sept. 11 attacks also filed lawsuits and won civil-damage awards it would reduce Iraqi resources that the administration wants to use to rebuild the country. Leitner and others say this explains Bush's reticence at this time to report the convincing evidence linking Saddam and al-Qaeda that has been collected by U.S. investigators and private organizations seeking damages. "The [Bush] administration is intentionally changing the topic," claims Leitner, and sidestepping the issue that "Iraq has been in a proxy war against the U.S. for years and has used al-Qaeda in that war against the United States."
I don't buy that argument. Timing appears to be the determining factor since unless it could be proved beyond a reasonable doubt the RATmedia would begin immediately to clamor that it is a lie.
It is unlikely that the Administration will be speaking of this until Summer to reduce the RATmedia's chance of dismissing it. There will be too many stories coming out then for it to concentrate on undermining this true connection.