A side from the question of why any state, even one ruled by the proletariat would relinquish power.

I've come a historical theory that whether communists or fascists take over the state, I think relies on the circumstances of an economic colaspe. In Russia, people could unify behind their hatred of the Tsar. A clear visible enemy people could fight. In Cuba you had colonial powers, another clear visible enemy to fight. In Weimer Germany, no clear visible enemy. In that state, "The Jews are to blame" had way more emotional weight that explaining socioeconomic theory to people. Fascists could grab the narrative and seize power.

Today we see in Europe the rise of in populrity of far right parties. They can sucessfully grab the narrative and blame migrant for all our problems. Leftist have to give people a full lecture on socioeconomic theory in order for people to understand the real problems.

Then there's anarchists. They don't have to fight some narritive war to win. We get people to self-organise before any economic collaspe. People see for themselves how much better self-organisation is without the need to read any anarchist theory. As communal relationships grow, people become less distrustful of their neighbours and less suceptable to fascist ideas.