Here's why:

* 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 its speed in water.

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

However, other properties of the wave can change upon reflection:

* Direction: The wave changes direction, bouncing off the surface.

* Amplitude: The amplitude (height) of the wave can be affected depending on the type of reflection. For example, a wave reflecting off a fixed end will have an inverted amplitude.

* Phase: The phase of the wave can also be shifted upon reflection.

In summary: While the speed of a wave remains the same upon reflection, its direction, amplitude, and phase can change.