It's not just about having a belief that their economic system is better, these people feel like they're possessed by cult like quasi-religious force, as were past ones like in the cultural revolution. It's the only way the current environment in the US makes sense because it's not logical whatsoever for this many people who grew up in Western countries to think having a revolution and replacing it with an ideology that's clearly failed is a good idea.
Why does this keep happening to human race? What is actually motivating them? Noting that these commies are insanely manipulative and dishonest therefore what they really claim to care about can all just be a front, like arguably the entire usage of race.
The "real commies" -- if by that you mean those at the top -- are sociopaths and psychopaths (who have frontal lobe dysfunction from serious repression, and frontal lobe deficits from genetics or physical damage, respectively) who have little or no sense of connection to others, no real empathy, and who see the world in a very different way than normal human beings.
Imagine being driven insane by lifelong solitary confinement ("no sense of connection to others") in addition to having been treated without respect or otherwise abused early in life.
You'd want something, ANYTHING, to cover up what that all felt like and to replace the utter lack of meaning your life had.
POWER. MONEY. CONTROL. The ability to cause PAIN to others with impunity. The feeling of being BETTER THAN NORMAL PEOPLE.
Those are the types of things that psychopaths and sociopaths crave, live for, and seek more than anything else.
Read The Black Book of Communism: Crime, Terror, Repression (by a group of mostly-Marxist lefties, not conservatives) and you'll see what I mean. Or if you don't read it (almost no one does, and it's $67 at Amazon), just meditate on the title. EVERY Communist nation has been a nightmare of torture, mass-murder, constant repression, and intentionally imposed poverty on the masses, with the wealth going to those at the top.