Here's why:

* Frequency refers to the number of waves that pass a point in a given amount of time. While frequency is related to the energy of the waves, it doesn't directly measure the speed of individual particles.

* Crest is the highest point of a wave. It's a spatial feature, not a measure of particle movement.

The speed of particles within a wave is often referred to as particle velocity, which is a component of the wave's overall speed.

Let me know if you have more questions!