Here's why:

* Temperature is a measure of the average kinetic energy of the particles within a material. Kinetic energy is the energy of motion.

* Mass is a measure of the amount of matter in an object.

While a large object will have a lot of total energy, its temperature doesn't directly increase with mass.

Here's an analogy: Imagine a small room with 10 people jumping around, and a large room with 100 people standing still.

* The smaller room has a higher *temperature* because the people are moving more, even though there are fewer of them.

* The larger room has a higher *total energy* because there are more people, but the *temperature* is lower because they're not moving as much.

Key takeaway: Temperature is about how much the particles are moving, not how many particles there are.