* Mass Difference: The Earth is vastly more massive than a ball. Since the force of gravity depends on the mass of both objects, the Earth exerts a much larger force on the ball than the ball exerts on the Earth.
* Inertia: While the ball accelerates noticeably due to Earth's force, the Earth's acceleration due to the ball's force is incredibly tiny. The Earth's enormous mass means it has a huge inertia, resisting any changes in its motion.
* Earth's Motion: The Earth is already in constant motion (orbiting the sun, rotating on its axis). The tiny force from a dropped ball is practically negligible compared to these other forces.
Think of it this way: Imagine a giant and a tiny person holding hands. The giant can easily pull the tiny person, but the tiny person pulling on the giant would be nearly unnoticeable.
To detect the Earth's motion:
While you can't see the Earth move from the ball's force, extremely sensitive instruments can measure the tiny gravitational pull of objects, including a dropped ball. This is how scientists can map gravitational fields and detect the presence of massive objects.
