Because socialism is based on big industry and big industry did not even predominate yet in 1921 Russia. There could hardly even be said to be “commanding heights of the economy” because even the biggest enterprises played a minor role in the economy. It was a largely peasant country overwhelmingly dominated by small commodity producers and petty-bourgeois enterprises.

The question arises: What elements predominate? Clearly, in a small-peasant country, the petty-bourgeois element predominates and it must predominate, for the great majority—those working the land—are small commodity producers.

It took time for the size of the proletariat to grow and the size of public enterprise to grow enough so that the public sector could actually be meaningfully said to be the mainstay of the economy. Even the little bit of big industry they had, some of it was stalled due to the war.