Read even the wikipedia article on the Kyoto Protocol and you can see why the U.S. wouldn't really want to sign it.
Not caring about reducing emissions has nothing to do with it. It has a lot more to with that it doesn't require other countries, like China, to do jack shit despite being on track to overtake the U.S. as the largest producers of carbon emissions.
Quote (of Bush) from that article:
This is a challenge that requires a 100% effort; ours, and the rest of the world's. The world's second-largest emitter of greenhouse gases is the People's Republic of China. Yet, China was entirely exempted from the requirements of the Kyoto Protocol. India and Germany are among the top emitters. Yet, India was also exempt from Kyoto … America's unwillingness to embrace a flawed treaty should not be read by our friends and allies as any abdication of responsibility. To the contrary, my administration is committed to a leadership role on the issue of climate change … Our approach must be consistent with the long-term goal of stabilizing greenhouse gas concentrations in the atmosphere."
It's an easy thing to harp on, but really, if you start looking into it there are obvious reasons why some nations would be ambivalent.