>>182109
Several reasons, all of which are depressingly simple.
1. The structure of communist ideology requires all political (a term which here means "economic, social, and governmental") thought to be reduced to a dichotomy. "Us"–who are a priori ontologically correct–and "Them"–who are a priori ontologically incorrect. "Them" is defined by "Us" and not by the people themselves. It cannot be allowed for anyone other than "Us" to define themselves.
2. The reduction of all political thought to two options allows for the next step of communist ideology–synthesis. In true Hegelian fashion, a Thesis is first presented. This Thesis is "everything we want." Then an Antithesis is presented, which is "everything we do not want." Note particularly that the Antithesis is NOT presented by "Them." The Antithesis is presented by "Us" and projected onto "Them" as "what They believe" (because We say so). Because this is a false dichotomy, "Us"–the communists–then refuse to accept any suggestion that other options exist. Only the Thesis and Antithesis are possible. No other positions can be held, nor will be entertained or acknowledged. Further note that the Antithesis is universally A. not representative of the world as it is right now; it's always closer to the Thesis than the current state of affairs and 2. peppered with outlandish, well-poisoning claims (which no one in the society wants to implement) which damage "Them" via guilt by association.
3. Then, with "both" "sides" presented, "Us" offers a Synthesis. "We are willing to compromise," they say. "Here, if you give us concessions on [these things], we will not impose the full extremity of our Thesis position." "Them," due to impotence and infighting by being forced together by their enemies, always accept the Synthesis and the "compromise" universally shifts society toward communist doctrine and what "Us" wants, never toward what any part of "Them" wants.
4. Oh, and for the sake of your question, there must always be a boogeyman. Always. Since God has been killed and religion no longer exists, Hitler has supplanted Satan Himself as ultimate evil in the world. Since no one can be more evil than Hitler, and since Hitler is dead, he must have minions to continue his bidding in the world. And since objectivity means nothing to a communist, and since "Them" consists of merely "literally everyone who does not support everything we support to the fullest degree that we support it," they can hand pick a representative out of "Them" against which to rally their forces. They need a figurehead, because that's how human psychology works. In 1984 it was Emmanuel Goldstein, the antithesis of Big Brother. In the "end of history" postmodernist liberal democracy world right now, it's Donald "All of my grandchildren are jewish" Trump, who is a genocidal white nationalist because "Us" said so. Donald "I have publicly said that US military should extrajudicially murder anyone who does not worship Israel." Trump has been hired to represent everything that communists do not represent, despite himself publicly supporting 6 of the 10 planks of the Communist Manifesto.
Why? Because popularity contests always need a figurehead. And when all media is owned by the same people, narrative becomes reality since no dissent is allowed to be visible.
That's the short version.