But seriously, why didn't communism triumph in the 20th century when things were looking so good? If the russian revolution and chinese revolution can succeed, liberating 800 million people, 1/3rd of the world's population, defeat the nazis, why couldnt we finish the final stretch? What was the fatal flaw?
Structural issues in the party system that led to a bureaucracy that could not respond to threats coherently or effectively and a military that could coup the gov with just a few jerks at the top consenting - with zero answer by the people to restore the revolution.
The government needs to be structured around the people such that it is not only responsive, but is responsive precisely because incentives align with the people's consent. Not capitalist incentive, but still material. Not bourgeois electoral consent, the threat of more engagement and involvement such that those in power are displaced by those with an interest in maintaining the line. Democracy that filters up through party activism and the necessity of regional coordination.
The USSR's bureaucracy stagnated and consequently aged out. The gerontocracy wasn't bad just because old people start losing their minds, it was a symptom of a system that depended on central administration but could not constantly replace its staffing, let alone ensure that said staffing had coherent theory behind their positions and actions. The gerontocracy was just one signifier of a deeper rot in engagement with the party and the accessibility of power structures.
So when some jerks at the top did a lib in times of decaying material conditions, there was nothing left to defend the revolution.
I think lenin proposed doubling size of central committe before he died but it never happened