For one, people are generally unaware of how much of what metastasized into Marxism-Leninism has it's roots in the Liberal West. Communism was implemented elsewhere, but it was dreamt up here. It was popular with with Jews so, in the West, it was protected against rebuke under the same umbrella. In turn, at the fall of the Iron Curtain, efforts toward something analagous to the Nuremburg trial or a version of "de-Nazification" was never implemented. By that time, the gravity in the Left had shifted to the 4thist Westerners who say dumb shit like "that wasn't real communism" anyway.