Because they weren't shocked and awed enough

We did this to the Iraqis: (Via No Capital, The Guardian):

Despite their prohibition under several international treaties and by the Geneva conventions, white phosphorus and a napalm derivative were used without discrimination on the civilian population of a city the size of Edinburgh throughout 2004.

[snip]

Few people know about the crimes committed during the two sieges of Fallujah - Operation Vigilant Resolve, launched three years ago tomorrow, and Operation Phantom Fury, in the following November - as a result of which 200,000 people became refugees. There are no official figures for civilian deaths.

In the face of repeated independent verification, US forces have now acknowledged the use of chemical weapons, and yet there remains no sustained international outcry and no official response (let alone condemnation) from any government or the United Nations. The US has overthrown a regime while supposedly searching for phantom weapons of mass destruction, only to use such weapons on the newly "liberated" civilian population. The cold hypocrisy of such actions is outweighed only by its extravagant viciousness.

Seventy articles of the Geneva conventions were breached in the two separate months of siege warfare.