Here's why:

* Mass vs. Weight: Mass is a fundamental property of matter, representing the amount of "stuff" in an object. Weight, on the other hand, is the force of gravity acting on an object's mass.

* Gravity's Role: Gravity pulls objects towards each other. The strength of this pull depends on the mass of the objects and the distance between them. A more massive object exerts a stronger gravitational pull.

* Constant Mass: While gravity influences weight, it does not change an object's mass. An object will have the same mass on the Earth, the Moon, or in space, even though its weight will be different in each location.

In summary: Gravity causes objects to accelerate towards each other and influences an object's weight, but it doesn't change the object's fundamental property of mass.