The revenue chart is worthless when it comes to showing demand for music. In fact it just demonstrates the music industry's rent seeking. They managed to maxim

The revenue chart is worthless when it comes to showing demand for music. In fact it just demonstrates the music industry's rent seeking. They managed to maximize their revenue when they had sole control of distribution. For most musical acts an "album" is one or two singles with a bunch of filler. Anyone wanting to buy those one or two singles had to spend $8-15 on a cassette or CD. When iTunes et al came around making single sales widely available, we get to see how little most people cared for albums. Before iTunes most labels didn't even sell singles and when they did they were still several dollars vs the 99¢ from iTunes and the like. Allowing consumers to actually buy what they want has been a huge improvement for them.