The format of the article was that of a critique. The author described how systems currently operate in a manner he viewed as deficient and then suggested ideas for improvements.
When the author states "the principal function of most corporations is not to maximize shareholder value, but to maximize the standard of living and quality of work life of those who manage the corporation", the author was implying that this is wrong.
They then stated that "Employees have a much larger investment in most corporations than their shareholders. Corporations should be maximizing stakeholder, not shareholder, value to employees, customers, and shareholders."
Thus the author semantically implies that "employees" are a separate group of persons from "those who manage the corporations". If employees and "those who manage the corporation" were the same group of persons or part of the system, then it would not have been necessary for the author to claim that corporations should also maximize value for employees, they would have only mentioned customers as the excluded group of stakeholders.