Over at Volokh, Ilya Somin summarises Paul Hollander's WaPo op-ed on the fall of communism. Hollander's longer article on the topic is also worth reading. Why victims of the Holocaust should be remembered and studied so much more than the victims of communism is indeed a bit puzzling. Hollander's explanation is as good as I've seen.
I would add three other points that I seldom or never see mentioned. A) The Nazi focus on Jews creates a narrative focus that sticks more easily in the mind. The Nazis also killed Gypsies, homosexuals, Jehovah's Witnesses, and the disabled, but the percentage of victims was so overwhelmingly Jewish that it creates its own movie script out of history. The communists killed more Jews than Hitler, but they also killed a few dozen other ethnic and religious groups. The very broadness of their evil seems paradoxically to lessen its impact on our psyche. B) Americans did not grow up with much knowledge of the places under communism in their formative educational years. We learned first about America, second about Western Europe. We might also have picked up something about Canada or Mexico. When we learned about Greece or Bible lands, it was the ancient history of these peoples, not their current incarnations. We otherwise had more misinformation than information on the rest of the world. Thus, when the countries of Eastern Europe were liberated, it was almost as if people had been added to the world. We hadn't been much aware of them, knowing more about Polish-Americans than people in Poland. As additions, these Eastern Europeans did not stick in the mind, and still don't. We had some awareness of Russia because it was so large and they seemed to be in charge of this whole Soviet thing. East Germans we could vaguely incorporate because we already had a cuphook for "Germans" in our memory storage. But who knew or cared about Estonians, Belorussians, or Moldovans, and who cares now? Europe was the UK, Germany, France, and Italy, then a bunch of others.
Ironically, the countries behind the Iron Curtain, who perpetrated or at least witnessed much of the Holocaust, had much of their own history concealed from them, and don't tend to think of the Jewish perspective on WWII that much.
C) and perhaps most important, the Jews had better writers and movie makers.