The best insights into why communism fails are provided by the tragedy of the commons and the prisoner's dilemma. If everyone receives an equal share of the wealth regardless of their contribution, and if making a contribution incurs a cost, then there is no point in contributing.
Some say that communism has been show to fail. Others say that that it has never been tried. Others say that it has been tried, and it has collapsed immediately every time.
Pedantry aside, the experiment has been done. It failed economically. It failed militarily. It failed morally. Time to move on.