For the same reason it's often said that the Soviet Union wasn't really communist since it turned into a dictatorship under Stalin. But that's what happens when communism is tried: because the absolute ideal isn't practicable, you need the gulags and a dictatorship to manage what the communist ideal leaves behind in reality.

It's the same with capitalism and democracy: when you apply those ideals, you eventually get something like the American free-for-all, complete with the severe economic inequality, the plutocracy, the private sector's capture of the public sector, the demagogery, and so on. That's just what happened to Russia after communism.

Why should we expect the real world to reflect perfectly an ideal? Ideals are imaginary simplifications, but the real world doesn't simplify: it remembers every hair on your head and every dust particle on every unclean surface.