It’s more so private production alienates the worker/laborer from his work/labor, thus someone owns a business or factory and hires people to make widgets, the workers make the widgets but have no ownership or influence over the widgets themselves, they are disconnected from “owning” their work.
The belief is based on that capitalism is an unnatural heirarchy, as where the worker works, those who manage the workers don’t work as they do, and the privilege and income starts from the top down. The owners of the resources reap the income of the workers making widgets, of which they have no authority over. Generally those who hold this view see the manager as unnecessary and generally association or ownership by contract irrelevant and void.