Timothy Snyder discusses this a bit in Bloodlands. His argument was that it was because Auschwitz wasn't purely a killing facility (like e.g. Treblinka) and left behind more witnesses, it became better known because there were simply more people to tell the story (and many of those stories, such as Elie Wiesel's and Primo Levi's, became well-known in the west). I don't know of a study that's specifically dedicated to that question, though, so you have some space to create new historical knowledge!

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