* Clear Starting Point: The ground level provides a clear and unambiguous starting point for measuring the ball's motion.

* Consistent Measurement: You can consistently measure the ball's displacement (change in position) relative to the ground.

* Simplifies Calculations: Using the ground as a reference point simplifies calculations of the ball's potential energy and kinetic energy.

While you could choose other reference points (like the initial position of the ball or the highest point of the bounce), using the ground as the reference point makes the analysis of the motion much more straightforward and consistent.