There's also been quite a few smaller socialist and anarchist societies that have existed under similar external influences. Almost like capitalism is tied up with ideological warmongering or something.

But 2 large economies tried to impliment communism… while engaged in a cold war against much more entrenched ideologies, while having corrupt leaders and they didn’t do it well.

And while - which I, personally, think is the biggest reason - starting from pre-capitalist economies, thus materially having to do what capitalism did (rapid industrialisation, disenfranchisement of peasantry, accumulation of capital), and ultimately following what Marxism would have guessed: Their ideology forming around their material reality of having to accumulate capital from labour while trading on the world market. So it basically became its own kind of welfare state/social democratic capitalism, with a bit of "but communism will arrive eventually, we promise!"

Once that material dynamic is entrenched, no amount of ideological purity can simply correct it from the top, you can't change material society by implementing an ideal onto a reality. It has to develop materially and dialectically, through the process of the old system failing (in unbearable ways), necessitating revolutionary changes.

Ones doing quite well, hence why countries are abandoning the US as a trade partner and going for it instead. Dengism is the solution to the failed ideal that you can take an agrarian preindustrial society straight to communism. And given all essential sectors are worker owned, it seems to be working.