Employees can loose the control of their corporation, or maybe never have it.
At least, a cooperative guarantees employees control for a long term. Any more, it is current that managers have more stocks than the others employees. Maybe someone think Bill Gates should have more rights. Anyway, the final objectif for an employee who has some stocks is often to saving money for his retirement, not really to effect a control on the management of his corporation. A member of a co-op just wants to manage his work tool.