That version of "real" socialism has always failed because the central planning of all economic activity is too complex. The management of all those details breaks down and you end up with queues for food, waits for services (or non-existence for some services), black markets, gangsters, corruption, etc. The invisible hand of the free market is a real thing, and it handles that complexity by itself automatically. Planning is distributed to every producer of goods or services, and every consumer.

It's actually a classical math problem: The number of economic interactions goes up exponentially as you add actors. Beyond a family or a tiny village it just gets out of hand. There is no escaping reality. Even our supercomputers are not up to managing all the economic activity of a US or USSR. So to avoid the horrors of raw capitalism, we end up with a mixed system. Capitalism drives most economic activity and government keeps capitalism from killing us to make soylent green. It isn't that we like the mixed system: Neither capitalism nor socialism work on their own.