Here's why:

* Scalar quantities have magnitude only. Examples include temperature, speed, and mass.

* Vector quantities have both magnitude and direction. Examples include velocity, force, and displacement.

Electric potential energy represents the amount of energy a charged object possesses due to its position in an electric field. It doesn't have a direction associated with it.

Think of it this way:

Imagine lifting a book from the floor to a shelf. The higher you lift it, the more potential energy it has. The potential energy depends on the height (a scalar) and not on the direction you lifted it (up, down, sideways).