The Constitution makes no mention of a Cabinet, but most Presidents tend to rely on their Cabinet members' advice and opinions. Why do you think that is?

The Cabinet members are the most knowledgeable in their respective departments.

Explanation:

The President frequently prefers members of the cabinet due to their reputation or to give his cabinet some form of racial, gender, religious and ethnic balance. The preference for the members of the Cabinet also lies because of their areas of expertise which would contribute much to policy making areas in their subjective fields.