Productivity under communism is punished. People learn quickly that scarcity is what produces value which can be traded for other scarce goods or services. A butcher makes meat scarce so she can trade it for a scarce medical service or a scarce set of used tires. Bus drivers go on strike or slow service to make their service scarce to get a raise of useless money or a useful privilege. All sectors are on the scarcity downward spiral until it grinds to a halt and the government can no longer function. It can happen fast, like in Venezuela. The Soviet Union kept it going longer through outward expansion and at home terrorism of the population. At a certain point, even threats of imprisonment and death won't make people work harder than the absolute minimum.