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 depends on factors like temperature, density, and pressure. The amplitude of the sound wave doesn't affect these properties.

* Amplitude is energy: Amplitude represents the maximum displacement of particles from their equilibrium position. It's a measure of the wave's energy. A higher amplitude means more energy, but it doesn't change the wave's speed.

Exceptions:

There are some exceptions to this rule in specific cases:

* Non-linear waves: In certain types of waves, like large-amplitude waves in shallow water, the wave speed can be slightly affected by the amplitude due to non-linear effects. These effects are less significant for smaller amplitude waves.

* Waves in dispersive media: In dispersive media, the wave speed can vary with frequency (and therefore wavelength), which can indirectly be affected by the amplitude if the amplitude modulates the frequency spectrum of the wave.

In general, though, for most common types of waves, wave speed is independent of amplitude.