"I oppose the Kyoto Protocol because it exempts 80 percent of the world, including major population centers such as China and India, from compliance, and would cause serious harm to the U.S. economy."
The above quote by George W. Bush clearly states The United States' reasons for not ratifying the Kyoto protocol. It only called for cuts for industrialized nations, not industrializing, which the U.S. viewed as unfair.
It is also believed that ratifying the Koyoto Protocol would have cost the economy around $400 billion, which would have been accompanied by a loss of 4.9 million jobs.