Why has an economic system run solely by workers and citizens never been realized?

The corporate system divides people between those who assume the responsibility of leadership of groups of people and those who self - lead. These entail different levels of responsibility, whether widget factory line worker, middle manager or high level executive.

There is no class distinction to be drawn between worker, middle manager or executive. It comes down to:

People's preparedness to assume the responsibilities of higher management or leadership

Other people's preparedness to trust in their leadership or the output of their endeavors

Unless a workers paradise is some distopia where workers don't need organisation or responsibility, the answer is simply, a lack of confidence in self or others.