Here's why:
* Freefall means the only force acting on the object is gravity.
* Gravity acts on objects with mass. The more mass an object has, the stronger the gravitational force on it.
* Mass is a fundamental property of matter. It's a measure of how much matter an object contains.
So, while the object's weight (the force of gravity acting on it) might change depending on its location (like on the moon vs. on Earth), its mass remains constant regardless of whether it's falling or not.