This is because modern manager's role is wide and varied. In short, there are three role categories: Interpersonal, Informational, and Decisional.
Interpersonal role is a role that represents the manager's interpersonal skills. For example, the manager maybe required to represent the organization to those outside the company. Thus, the manager acts as a liason of the organization. The manager also has to provide leadership role to his subordinate and a symbol that represent the organization (figure head role).
Informational role demands that manager not only to gather data from his subordinate, and to act as a monitor, but also to spread news to his subordinates (disseminator role). In addition, he also must provide public information about his organization to the public at large, which means that he must also fulfill his spokesperson role.
Decisional role has always been and always will be required that of a manager. In this role, the manager may make the strategic planning of the organization (entrepreneur role). While enterpreneur role may occupy most of his time, there may be times where the plans must be put into actions. In this case, he will allocate the resources of the organization in the manner best possible. Of course, there are inevitable times when his subordinates may have conflict over the orders. The manager will then handle the disturbance among his subordinate. And when the required orders necessitate contact with those outside the company, for example, customers and suppliers, he must also fulfill the negotiator role and attempt to get the best deal...