The authors of the Constitution envisioned a president above partisan politics. In George Washington, they chose an individual who scorned political parties, calling them "potent engines, by which cunning, ambitious, and unprincipled men will be enabled to subvert the power of the people and to usurp for themselves the reins of government."
They hoped that Washington's successors would emulate his example. They were wrong. The system they created encouraged, if not demanded, a rise of political parties to articulate and broker differences, and required successful presidents to be effective party leaders. For political parties, the presidency is the highest prize. There are coattails to ride into office, and there is patronage to dispense to the "boys."