The reason is the same as always, extraction of natural resources and cheap labour from Russia.
Europe will never side with Russia in this conflict, but should the US attack China, Europe might side with China in hopes of regaining independence from the US.
[...] when Hitler Germany declared war on the Soviet Union, the Anglo-French-American bloc, far from joining with Hitler Germany, was compelled to enter into a coalition with the U.S.S.R. against Hitler Germany.