And then, there's a question of whether Soviets would expose it any time soon - even with USA in the game, taking Moscow is hardly an easy task when your starting positions are somewhere around Flanders; And prolonged war means more chances for communist revolution either within allies or within Allies.
They are not even in Flanders. Closest Allies troops of Moscow currently are in Northern Sweden/Norway. Not greatest places to begin invasion to Russia. Them should even get good foothold on mainland Europe firstly and Germans have now more troops since they are not tied to Eastern Europe.