Probably because people who study Marxism realize the difference between communism and totalitarianism.

The USSR had Totalitariansim - a combination of fascism and socialism. It never had communism.

Communism has never actually excited. In communism, there is no government. The people own different means of production - so one group would farm food in this geographical area and another would build machinery in that area, and they would all cooperate with each other.

The Russian Revolution inteneded to evolve into communism but never did. That was because those who obtained power loved it and never wanted to let it go.

I'm not quite sure why so few don't realize that Russian misnamed itself - the political system waas totalitarianism.