Why are political/appointments short-lived?

Political appointments are short-lived in order to prevent autocracy, tyranny, and clinging on to power.

Explanation:

Power corrupts and absolute power corrupts absolutely. Humans have a tendency to be intoxicated by power. This is why most political positions run for just a few years after which the people can determine through voting on whether they will continue with the appointee or elect another person. The presidential and senatorial sectors of the United States democracy follow this system.

Presidents are allowed 4 years in office after which another election is conducted to determine their remaining or being removed. This prevents tyranny and the imposition of the opinions of a few against the majority.

answerequity law;