An interesting question at face value, but very simple in practical application in the modern day, and also explains why it didnt catch on in the past
Specifically, jealousy and greed are the answers. These "activists" who stand outside chanting shit and claim to want everyone to be equal and share everything, do so because they are greedy and see a vast ocean of "wealth" in front of them that they want for themselves. But they are inept and useless and thus earn basically nothing, they are jealous of everyone who is better than them, who works harder, who earns more, who has a better life, and they greedily want that for themselves. BUT they are incapable of obtaining it, they're stupid, or lazy with no work ethic, they have no will power to actually work to achieve anything, and thus their only means of obtaining the things they can see and covet is if the state or commie block GIVES it to them because "theres enough to go around."
But being stupid, they dont understand that "wealth" is not just magicked up by the state. Wealth is how we measure the productivity and output of a nation, but that value comes from the workers who create produce or serve. If there is no creation/production/service then there is no value/wealth to be had. A unit of currency only means something if it is backed up by the economic activity of a nation. And if you go around handing currency out to everyone equally despite being useless fucks like them, then more and more people are going to jump on the "might as well be a useless fuck and still get paid" train, because why work if you're equal with the guy who doesnt? And the system stagnates and collapses rapidly because comrade bret thinks hes entitled to the fruits of comrade johns labor, then john stops laboring to leech off comrade jacks labor and so on and eventually theres no more wealth because theres no more production, and as that happens the overall wealth continues to drop and the things to go around continues to dip into nothingness.
Whittle did a video about this at one point, but the highlight was he noted some shitty little village with a disgusting water supply going through it, and the question "why does no one improve it? why does no one build a road or a better home?" And the answer is simple, why put that effort in if the fruits are going to be handed out to everyone? Where is the compensation for all your hard work? Why do the work yourself? Why not just see if someone else does it and then get the benefit without any of the work?
Its jealousy and greed that drive them, and stupidity and laziness that put them in a place where they would be so greedy/jealous. And the reason this never worked in the past was simple, what wealth was there to go around? Income disparity wasnt as large as it is now, and people had a strong work ethic to improve their own lives and had the means to achieve it. Thus, while greed and jealousy existed, the cultural view was "go work your ass off and earn what you want, its possible."
Now though? With Obama destroying our economy, helping to increase income disparity then playing the "benevolent state" by increasing welfare, absolutely fucking most peoples ability to even learn, much less get a good job because there are none or theyre all given away to poo in the loos, more and more citizens are stupid and lazy (coddled by state hand outs), and all they can see is what they dont have as its shoved in their face 24/7, but even if they were harder working theres just not enough to go around thanks to obama and his ilk. Thus they're left with nothing to do but whine for more handouts and to steal from the rich. All according to plan really.
So like I said, interesting question at face value, but simple answer. Greed and jealousy bred out of stupidity and laziness, pushed on the nation by a president and political class hell bent on destroying the nation from within.