It works not in theory, but in practice. And the main reason is the freedom inherit in swapping goods for money by the 2 sides by their own will. The freedom to choose where to invest your money gives the capitalism inherently more freedom that any other centralized system of distribution.

Communism can't work because economic inefficiency kills the system. Look at Russia and Ukraine now, during Soviet times after 1970 they imported grain, now they're one of the biggest exporters. It's not only technology, it's the "capitalism" at work.

In USSR, only 3% of land produced almost all fruits and vegs in the market, because the collective farms were given the permission to allow private land use and selling of produce on the market. They needed to give the collective farm a certain percentage of the crops, but what they kept they could've sold. Again capitalism at work... Efficiency was trough the roof.