Here's why:

* Wave speed is determined by the medium: The speed of a wave is primarily determined by the properties of the medium it travels through. For example, the speed of sound in air is different from the speed of sound in water.

* Reflection doesn't change the medium: When a wave reflects, it simply changes direction. The medium it travels through remains the same.

However, other wave properties can change during reflection:

* Amplitude: The amplitude of the wave (its height) can change depending on the properties of the reflecting surface.

* Phase: The phase of the wave can shift by 180 degrees upon reflection, depending on the type of boundary it encounters.

* Direction: The direction of the wave changes, of course, as it bounces off the reflecting surface.

In summary: While the speed of a wave remains constant during reflection, other properties like amplitude, phase, and direction can change.