Communists (in the marxist sense) definitely take a systems thinking gear like approach, not a magical "evil people do evil things" approach.

True for textbook Communism, but it doesn't work for politicians. What is a Communist politician supposed to say to their voters: "Let's sit here with our hands folded and wait for the inevitable collapse of the capitalism"? They must point fingers. They must point fingers more than their competitors for the same role.

And when the Communists rule the country... they empirically can't deliver what Marx has promised. So they must find excuses. Stuff like "Socialism is the initial stage of the Communism, containing still some elements of capitalist system such as money; just wait a few years longer and you will see the final stage". In reality, you have a pseudo-capitalist system with a dictatorship of the Communist Party, state-owned factories and regulated prices, mandatory employment and press censorship... and you stay there for decades, because... well, again, you must point fingers. American imperialists, internal traitors, everyone is trying to destroy our 'freedom' and happiness.

EDIT: But probably more important than this all is that you have to "sell" Communism to people who are prone to magical thinking. So whatever the original theory was, as soon as it reaches the masses, your average supporter will think magically.