So why would a composer abandon beauty in a musical composition? Here we get to the second dichotomy in music: Interesting-Boring. If a composer used a very beautiful chord and repeated it 20 times, even if it was the most beautiful chord in the world, your mind would probably start wandering or you would change the track in your device. Music has to be interesting. The composer has to engage his listener. This might actually be the most important dichotomy. Throughout the history of music, changes were introduced in the most part to make it interesting. That is the origin of the language of XX century music. It got really dissonant and the structures were changed radically because the sounds that had been used in the XVIII and XIX century had been used so much that even though they were very beautiful, they were boring to the composers. They were also boring to parts of the public particularly to the true connoisseurs, and to some of the critics. That explains the rise of atonal music and the backing it received in some critical circles.
Now, in popular music the lyrics of a song contribute greatly to the interest of the song but in classical instrumental music, we have to create interest in different ways. And so we get to the third dichotomy: