Here's why:

* Mass is a fundamental property of matter that represents the amount of "stuff" in an object.

* Gravity is a force that attracts any two objects with mass. The more massive an object, the stronger its gravitational pull.

* The force of gravity between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

So, the greater the mass of an object, the stronger the gravitational force it exerts and the stronger the gravitational force it experiences from other objects.