Here's why:

* Mechanical waves require a medium: They need a material substance like air, water, or a solid to travel through.

* Energy transfer: Mechanical waves transfer energy from one point to another. Think of a ripple in a pond – the water molecules themselves don't move far, but the energy of the wave does travel across the surface.

* No matter movement: While the medium particles oscillate or vibrate, they don't travel long distances with the wave. They simply pass the energy along.

Examples:

* Sound waves: These travel through air, causing air molecules to vibrate. The vibrations carry the sound energy, but the air molecules themselves don't travel with the sound.

* Water waves: These travel across the water surface, causing water molecules to move up and down. The wave itself moves forward, but the water molecules mainly oscillate in place.

Let me know if you'd like more detail on a specific type of mechanical wave!