I kinda had the same thought but then read a really insightful article about how China's long term play here is really about expanding their influence throughout Asia.

China is far ahead of us in terms of alternative energy development (one trip to any Asian capital and all you'll see is Chinese electric cars, and Chinese sponsored energy projects)... skyrocketing oil prices and supply shortages, while they will negatively affect some Chinese industries, actually play to China's long term regional interests.

I believe this is why they haven't gotten involved in any meaningful way. They're playing the long game and letting us continue the process of bleeding ourselves that began with the invasion of Iraq and continues today.