Here's why:

* Enthalpy change is a state function: This means it only depends on the initial and final states of the system, not the path taken.

* Catalysts change the path: A catalyst provides an alternative pathway with a lower activation energy, speeding up the reaction. However, it doesn't change the overall energy difference between reactants and products.

* Energy conservation: The total energy of the system remains constant, even with a catalyst. The energy released or absorbed during a reaction (enthalpy change) is independent of the catalyst.

Think of it like this: Imagine a ball rolling down a hill. The catalyst is like building a ramp, making it easier for the ball to get to the bottom. The ramp doesn't change the difference in height between the top and bottom of the hill (enthalpy change), it just makes the journey faster.

In summary: Catalysts affect the rate of a reaction, but they don't change the enthalpy change (heat released or absorbed) associated with the reaction.