Here's why:

* Mechanical waves are disturbances that travel through a medium. The medium can be solid, liquid, or gas.

* The particles of the medium vibrate or oscillate. These vibrations transfer energy from one particle to the next.

* Without a medium, there's nothing to vibrate. This means there's no way for the disturbance to travel and carry energy.

Examples:

* Sound waves: These travel through air, water, or solids by causing vibrations in the particles of these mediums.

* Water waves: These are caused by disturbances in the water's surface, which then propagate outwards.

* Seismic waves: These travel through the Earth's crust, mantle, and core.

In contrast, electromagnetic waves (like light) do not require a medium to travel. They can travel through the vacuum of space.