Saddam did kill a whole bunch of Kurds in the 1988 Anfal campaign.

But it's not as open and shut because he wasn't there and there may not have been any documents with his signature on them ordering the campaign.

Why take on less sure cases when you have an atrocity that he was actually present for?

Now Chemical Ali, they'll nail him for the Kurds for sure, because he was the primary guy in charge on the ground at the time.

They can also get Chemical Ali for the way he governed Kuwait during the Iraqi occupation. Something like 5000 Kuwaitis disappeared during just a six month period.