The entire foundation of Marxist thought was that the economies in question were industrialized, productive, and developed. Those were, Marx argued, the circumstances for which the progression towards socialism would be natural.
Look now at when socialist revolutions occurred and the state of those countries at that time. It’s difficult to argue that those countries were industrialized, productive, or developed.
Lenin and Mao were running off script. According to Marx, every country must transform it’s peasants into proletarians. Historically, this had been done through a period of capitalist development. How do you pursue socialist ideals in a country of peasants?