Why does the gravitational force obey an inverse square law?

the gravity force obeys the inverse square law because according to the newtons law of gravitaion the force of the gravitation is directly proportional to the product of masses ... In this way it depends upon the masses directly. We donot notice any gravitational force because we have very small masses as compared to the plantery universe and the solar system ... due to there greater masses they exert a large force and thus by increasing the distance the force of attraction varies inversely to the force of gravitation ... thus gravitional force is a variable quantity ... varies inversely to the square of distance between the to bodies ...

F ∝1/r2