why are the presidential cabinet and political parties called part of the unwritten constitution?

The Constitution doesn't mention the cabinet nor political parties. These grew out of needs that weren't foreseen or, at least weren't seriously considered, by the writers of the Constitution.

The presidential cabinet and political parties are considered part of the unwritten constitution because they are not explicitly laid out in the formal written document of the constitution. The United States Constitution, which serves as the foundation of the American government, does not mention the existence or specifics of the cabinet or political parties. However, their roles and functions have evolved over time and have become core elements of the political system.

To understand why they are considered part of the unwritten constitution, it's important to recognize that the U.S. Constitution is a relatively brief document that outlines fundamental principles and structures of the federal government. It creates the three branches of government (executive, legislative, and judiciary) and provides a framework for their powers and interactions. But it doesn't provide detailed instructions for how these branches should operate or the specific political processes that would develop over time.

The formation of the presidential cabinet and political parties arose out of practical necessity and political custom rather than from explicit constitutional provisions. The cabinet is an informal group of advisors to the president, who head various executive departments. It developed as a means to assist the president in making important decisions and managing the affairs of the nation.

Similarly, political parties also developed outside the constitutional framework. They emerged as organizations that sought to influence public opinion, nominate candidates for political office, and shape government policies. While political parties are not explicitly mentioned in the constitution, their existence and influence in the political process have become integral to the functioning of the American democratic system.

In summary, the presidential cabinet and political parties are considered part of the unwritten constitution because their formation and role are not explicitly outlined in the formal written document of the U.S. Constitution. Instead, they have evolved over time through political customs, practices, and necessity.