A very long time ago, an economist whose name and nationality I do not remember, said that all economies are capitalist. What differentiates Communism from Capitalism is who owns the capital. In Capitalism largely private ownership, in Communism, state ownership.
A better way to say it is “all people are capitalist”. A person only does things when they get something they value in return. This also applies when they get something intangible (“good feeling”, “heavenly reward”, “karma”, “descendants to carry their name”, “admiration”, etc) in return.
In Russia or in China, despite communism, people still do work, even (especially) if it’s additional work over the thing they are assigned by the state (or representatives of the state, like their employer), only when compensated for it in some way. And, conversely, they don’t do their best work when not compensated fairly (willing buyer/willing seller of labor too). Hence the old Russian joke “they pretend to pay us and we pretend to work”.