Here's why:

* Sound needs a medium: Sound waves are mechanical waves, meaning they require a medium (like air, water, or solids) to travel. They cannot travel through a vacuum.

* Different mediums, different speeds: The speed of sound varies depending on the density and elasticity of the medium. Solids are generally denser and more elastic than liquids or gases, so sound travels faster in solids.

* Solids vs. liquids vs. gases:

* Solids: Sound travels very well through solids because the particles are tightly packed and can easily transmit vibrations.

* Liquids: Sound travels somewhat well through liquids, but slower than in solids.

* Gases: Sound travels the slowest through gases because the particles are far apart and collisions are less frequent.

Examples:

* Vacuum: Sound cannot travel through a vacuum (like outer space) because there is no matter to vibrate.

* Plasma: Plasma, a superheated state of matter, is a complex case. While it can support some sound wave propagation, it's not a straightforward conductor like solids or liquids.

Therefore, while many forms of matter conduct sound, there are cases where sound cannot travel.