Speculation time: Why do you think there is such a fundamental difference between visual art, and music?

When you look at the visual art that is most popular, they are almost exclusively depictions of objects known in the real world, or objects that resemble real life counterparts or combinations thereof. Even the most recent pinnacle of visuals, Avatar, is an example of that. Trees, animals, tall blue people, people, machines.

When you look at music however, it is mostly an arrangement of sounds that are not found in nature, and humans invented instruments to produce these sounds, from violins and pianos to modern electronic music where these sounds are further distorted.
If music where like visual art, it would be an arrangement of sounds found in the real world, like dog barks, bird song, thunder, wind, water, car engines, gun shots, wolf howls, etc, but instead they are all sounds that have been invented by humans.
Conversely, if popular visual art were like music, it would be abstract art, and Avatar would have been animated abstract art, abstract colours and shapes that have no connection to the real world moving around and morphing into different shapes.

Why do you think there is this obvious fundamental difference in the natures of visual art and music?