I think the existence of forces coercive to free communities has a large part to play in them not lasting, as does the tension of coming from a world where we mostly don't have practice living the way we might want to, and so have to learn on the fly.
The collectives in Spain, the commune in Paris, the anarchist sections of the Ukraine, various utopian societies in the US (for example, Home, which is located very near Tacoma, WA but is now just a small town of beach houses) failed because of having to deal not just with the internal conflicts that will arise in any community, but also to defend themselves from, variously, the state, capitalism, moralism, and other external forces (literally in the cases of Catalonia, Ukraine, and Paris, and more ideologically in the case of utopian communities in the US).
And it is hard. Having lived in housing situations that attempted at living more communal, anarchist lives, the differences in values, long term goals, and priorities, matched with personality conflicts and the majority of us having to still have jobs because, you know, capitalism meant that while there were some shining and wonderful moments of us living and being our best selves (I am uncomfortable using "best", but I think that is the correct word) were punctuated with us being crabby, petty, and falling back in to the ways we were raised. And those were situations with between five and a dozen people. When we start looking at whole communities anthropologist Robin Dunbar put the number at about 150, the speculative utopian book Bolo'bolo places the size of an individual community, a Bolo, at between 300 and 500 individuals), the situation becomes even more complicated, as we will all be unlearning at different rates, as well as struggling with our varied desires and visions, even if we are talking about a group with a largely unified set of underlying beliefs or motivations.
I also think it is important to point out that for most of human existence, people lived in social arrangements that were largely harmonious and were mostly free of controlling systems and institutions. Mostly now we refer to these people as hunter-gatherers (gatherer-hunter is more accurate, and some incorporated other ways of subsisting as well). Some still exists, most have been wiped out by coming in contact with civilization (which requires expansion, resource extraction, and increasing degrees of centralization and control), or slowly became civilized through the adoption of agriculture and the related sedentary living arrangements (there are questions on this site where this critique of civilization is explored and when I have time I will try to find those questions and add links, but a good mythopoetic exploration of this process is contained in Fredy Perlman's book Against His-Story, Against Leviathan!).