Memes

Part of it is the initial conditions of states experiencing socialist revolutions, as those generally don't happen when things are going well, and fighting during the revolution itself will also destroy some infrastructure, so even the more powerful of those states start on the back foot. In addition, during World War 2 both China and the USSR saw major invasions by the axis power causing even more damage to them, while the mainland of the US did not see any fighting which allowed them to maintain their productive capacity and infrastructure. Due to these factors, the western powers did have more resources to inflict and resist sabotage. That is not to say that it was necessarily the only reason, but it was certainly a significant factor.