If a stone attracts the Earth, why can't the motion of Earth towards the stone be observed?
Acceleration of the Earth towards the Stone is much smaller than the acceleration of the stone towards the Earth.
Mass of the Earth is much larger than the mass of the stone.
The Earth and the stone experience equal gravitational forces from each other.
However, the mass of the Earth is much larger than the mass of the stone. Hence, the Earth's acceleration towards the stone is much smaller than the acceleration of the stone towards the Earth.
This is why the Earth does not appear to move towards the stone.