I wonder if that's because of communism or because in any country with one party in power for too many years there is a drift to authoritarianism first and eventually to dictatorship. There are examples even in Europe and around it right now.

Of course communism as ideology cannot allow competing not communist parties. That would be heresy and the first years after the revolution in Russia 100 years ago show how it goes. Not communist parties are unthinkable by definition so yes, an ideological communist country sets the stage for dictatorship. A communist party in charge for only a few years in a democratic country, not much more than anything else.