Because US managed to annoy all three to the point, that all three benefited from weakening the US position. Russia is more ambivalent, because we actually have reasons to be wary about China, too - but America managed to became our more immediate concern, than possible future alteration with China.
Has America grown into a concern because of Ukraine & Syria? I would think a rapidly developing military next to the Siberian Resource Reserves would cause some discomfort. AFAIK Russia is currently allowing Chinese companies/workers to extract resources from there.