Communism doesn't work because its originator (Marx) used Hegel's dialectical method, which was only ever meant to be used in conjunction with an idealist (=reality is derived from the mind) philosophy, and misappropriated it into dialectical materialism. The dialectical method is acceptable when the contradictions are between concepts during the process of gaining knowledge which if completed results in "the truth being the whole".

In materialist philosophy, the real world exists entirely outside the mind and the mind only interprets it. Having dialectical materialism would imply that material reality has a final destination (=communism) that it is striving to achieve and that rather than concepts such as life and death contradicting each other, it's people that are contradicting each other (capitalists vs proletariat). Because forward progress is guaranteed, there is no need to have knowledge/discussions about how to arrive at the final destination. The best way to accelerate the process is to simply destroy the existing order no matter what it is. Reformists (people who demand incremental improvements) are slowing down progress toward utopia while supporting the status quo and should be held in contempt.

What this ultimately means is that Marxist socialism has never been about building a good society for people to live in, but to dismantle the status quo, no matter what it is. This makes Marxist socialism an extremely attractive ideology for ruthless, violent or narcissistic individuals, while simultaneously luring in unsuspecting people who just want a better life and have reasonable grievances with the status quo. These subtractive ideologies fail because they're biting the hand that feeds them.

There is this socialist streamer (Vaush) that summarized all of this in a single sentence. "I don't care about principles, I only care about winning."