That's exactly the point. We knew about this in the 1990s, and it wasn't a justification for a war. We knew about it in 2001, when the sabers started rattling after 9-11, and it was never cited as a reason to invade. We knew bout it during and immediately after the invasion, and it was never used as an after-the-fact justification for the invasion. We're had troops Iraq all these years, and it has never, ever been used as an excuse for our continued presence.
So, why should it suddenly have any meaning whatsoever now that it has been removed from Iraq?