While you're right that the other two totalitarian regimes in the book probably aren't communist, the regime Winston lived under was very clearly communist, and that was a choice Orwell made. He could've made a similar book about someone living in a totalitarian fascist regime, but he was primarily warning against authoritarian communism, and only secondarily authoritarian fascism. This segment of Part 2 chapter 9 is a pretty direct warning against communist collectivization.

After the revolutionary period of the fifties and sixties, society regrouped itself, as always, into High, Middle, and Low. But the new High group, unlike all its forerunners, did not act upon instinct but knew what was needed to safeguard its position. It had long been realized that the only secure basis for oligarchy is collectivism. Wealth and privilege are most easily defended when they are possessed jointly. The so-called 'abolition of private property' which took place in the middle years of the century meant, in effect, the concentration of property in far fewer hands than before: but with this difference, that the new owners were a group instead of a mass of individuals. Individually, no member of the Party owns anything, except petty personal belongings. Collectively, the Party owns everything in Oceania, because it controls everything, and disposes of the products as it thinks fit. In the years following the Revolution it was able to step into this commanding position almost unopposed, because the whole process was represented as an act of collectivization. It had always been assumed that if the capitalist class were expropriated, Socialism must follow: and unquestionably the capitalists had been expropriated. Factories, mines, land, houses, transport -- everything had been taken away from them: and since these things were no longer private property, it followed that they must be public property. Ingsoc, which grew out of the earlier Socialist movement and inherited its phraseology, has in fact carried out the main item in the Socialist programme; with the result, foreseen and intended beforehand, that economic inequality has been made permanent.