One had to question why this was so. Mainly, structures of power, along with human greed, and the will-to-power, cut short any real investment in a communist society and economics. Another reason is that, along with invasive capitalist exploiters, capitalist countries and cabals, primarilly the USA, did everything they could to undermine the development of communism, & via socialism, in other countries, in Eurasia, Latin America, Indochina, Africa, etc.
After WW2, and Mao, there were good reasons to try to prevent any rise of socialist states elsewhere, because, in the American mind, communism = tyrannical state = moral and capitalist enemy, AND, communism = Atheism, for various real and imaginary reasons. To fight "communism", (which was really socialism, which was really statism), was to fight Godlessness. And this made things much easier to sell, especially to the USA, so rooted in a dynamic Christian past.
All these right or wrong prejudices systematically and forcefully sabotaged any rise of "communism" abroad or at home. In the process, the USA leaned towards becoming something of a Statist system itself, and this was reinforced both by the New Deal and Republican (and then Democrat) hawks. At home, agencies like the FBI, CIA, NSA, etc., often served purposes of the state which were more invested in power than in any kind of justice, economic theory, or protection of its citizens. In the USA, "morality" is often linked to rationales for expanding power, both personally and geopolitically.
Marx, himself, believed that, before any true communism was possible, first a given capitalist economic system must naturally self-destruct, under its own weight, and the working poor would then be elevated to power, especially through revolution. Whenever it was asked why no true communism yet exists, the answer was that no capitalist state had yet completed this (dialectical-materialism) transition.
But I think the two major reasons why true communism has not come to be are that an assortment of greedy capitalists get their hooks in before wealth and land can be given over to the workers, etc., and that the prohibitions exerted by the boycotts, etc., from other nations, and the influence of international currency standards, maintaining a status quo global power hierarchy, simply make it impossible for any communist state to gain independence and strength.
In the real world, true communism cannot exist, because of exogenous forces. BUT, could it exist in the real world IF protected by some theoretical bubble? Highly unlikely, due to human nature. Individual motivation would tend to be subdued by the call for altruist collectivist action, with a future less tangible, more abstract, than the selfish wants or deviations of any one individual. Thus, economic competence gradually decreases, while the solution to this problem becomes the rise of the state to further manage a dying economy, and to even-more-so subdue the tendencies towards individuality, through force, or by fulfilling economic needs of individuals and their families. Of course, this is a money-sink, a snake chasing its tail, and must eventually self-destruct, as had been prophesied to occur for the capitalist economies, ironically.
But, I have said, irony is also in nature. The reason why communist countries collapse before capitalist ones is the global conspiracy of capital, meaning choice, alternatives, and delusions - up to the point where the globe no longer accepts the anti-natural-future growth, and collapses capitalism on its own. Which is NOT something to look forward to.
The faults in both systems can also be analysed by looking at economics with a model of thermodynamic entropy, or by Entropistic Analysis. This is my own theory, but can approximated or approached through books by Jeremy Rifkin and Ted Howard, (see Entropy), and by going to my tags and looking up, "virtual scarcity", etc. The constraints on capitalist or industrial growth can be compared to writings of the Club of Rome, which conservatives saw as a communist conspiracy. Many of them were insistent that God would take care of nature for them just fine. (Today, many of that sort have come to see that, yes, Global Warming exists, and is at least party caused by humans).
In fact, the global constraints of nature are now such that they supersede whatever economic or social limitations which were seen to inspire communism or the drive to create communism. Indeed, Marx did not see this sufficiently, but those limitations do, themselves, have a natural genesis.
Its very simple: Where a growing population of people are allowed to get get get and grow grow grow for themselves, natural limitations arise, like the inability to increase crops, leading to a rising poor majority's demand for economic compensation or justice. In a sense, that is what is happening in the USA today, more in the arena of culture, and more demand-side than supply-side sociologics, but not without having economic connexions. Addressing the economics is what is most important, and this is why I maintain adherence to the OCCUPY movement, see o_c_c_u_p_y.
Capitalism is based on the idea that the strivings of self-interested individuals, in competition with each other, will build an increasingly beneficial, and fair, economy. Communism is based on the idea that collective cooperation will remove the limitations imposed by selfish individuals and gradually build a more equitable and efficient economy. Both are underwritten by moral ideologies.
In the first, government is needed to see that competition does not spiral out of control in a natural Tragedy of the Commons. The second needs government to manage the cooperation of citizens and to step in and compensate for the growing lack of individual dynamism. Both need government to protect themselves from the competing theory and system.
But, notice that the first addresses one aspect of humans, and the second addresses a seemingly contrary aspect, both making these their premise or a-priority. But, by doing this, each system eventually ends up mopping up after the consequences of alternate and oppositional human nature. Like Yin trying to deny Yang, and vice versa, and consequently being overwhelmed by what each had tried to deny.
Neither system starts off by welcoming both aspects of human nature. Or even, and especially: Of Nature itself. After all, both systems exist towards serving human needs. Not environmental, or animal, or even naturally logical, or spiritual. So, in the end, BOTH human systems should consequently be overwhelmed by what BOTH had tried to deny: Nature, both in humanity and in the environment. So, there remains one huge dialectic we have all yet to witness.
Note: For new readers. This post is one of my, "theme posts," and is part of a series. I usually write about cosmical ideas related to physics, time or consciousness. I have been to out of sorts in recent months to put my mind to such nonsense. You can find more of my (theme post) series by scrolling down in my tags to "s-", (or search separate topics).