Why does conduction occur more easily in solids and liquids, than in gases?

Because liquids and solids are denser than gasses.

Explanation:

Solids and liquids are denser than gasses making it easier for things like sound to conduct through them. Being dense contributes to a better conduction because the particles and such within the solid or liquid are closer together which allows for things like sound to travel at a much faster rate because they're so much easier to vibrate.