Capitalists in the West are quite a bit RESTRAINED by a body of law that has been built up by Environmentalism, over the years. It’s sort of disingenuous to say that these capitalists in the West are effectively “doing their thing” in an unrestrained manner.
China, on the other hand, doesn’t have that same body of law. There are capitalists in China, too - and the result you see there are how the capitalists work there under “that” body of law.
But China satisfies the liberal model because for liberals it's only the capitalist part of China causing the pollution.
“But, but, but I get to hear all the time how careless capitalists are with the environment and only communism can save us from this exploitation of our resources, air and water.”
Well, according to many American communists, the Chinese just aren’t ‘doing communism right’ - that’s where the problem lies.