Here's the thing ~ like it or not, believe it or not, popular music has not changed that much since the advent of rock and roll. It's true that hip hop has branched off during the interim, and that world music has claimed some attention. But musically speaking, there has been very little evolution, much less revolution, over the past half century. If anything, the lines that once distinguished rock from country from blues have blurred, so that each resembles the other.
A peer-reviewed study in Scientific Reports confirms my assertion. As reported at the website io9, the researchers found that "pop songs have become 'intrinsically louder' and have come to rely more on more of the same chords, melodies, and sound palettes." Which would be like all artists using the same narrow variety of colors, or all writers using the same restricted vocabulary. There's a word for the situation ~ stagnation.
Further, the study "obtained numerical indicators that the diversity of transitions between note combinations ~ roughly speaking, chords plus melodies ~ has consistently diminished in the last 50 years."
When you take a mental step back to regard music through history, you notice that the music people listened to is heavily correlated to the instruments being used, in addition to the creativity of composers. From the symphony orchestras of classical music, in the 1920s and 1930s we shifted to the smaller, sassier big band sound. Then in the 1950s and 1960s came the shift to rock and roll, shrinking the instrumentation even further, typically to three guitars and a drum set (with occasional variants like keyboards thrown in). The advent of synthesizers and digital music did little to change the limited tonality of the music being sold to us.
Perhaps money is part of the story. It's cheaper to front the costs of supplying instruments to a rock band, than it is to furnish a full 100-member orchestra. Similarly, an individual need not devote as much time to learning to play a limited range on a guitar, as she/he would to mastering the violin, French horn, or cello. Over time both performers and listeners have learned to take short cuts, and we are aesthetically the poorer for it.
Instrumentation and ensemble size aside, there's this to consider ~ in western popular music, the impetus for creative change has most often come from oppressed groups ~ in the case of the U.S., black musicians. Blacks invented jazz, swing, blues, and early rock and roll. White musicians knew a good thing when they heard it, and picked up the sound. Ask any white virtuoso musician about his/her influences, and chances are you'll be referred back to those old school black singers and instrumentalists, back in the day.
These days, even the pop music of my teen years sounds tinny to my ears. I'm drawn more to the expressive lyrics and music of my parents' generation ~ the standards of the 1930s and 1940s ~ and drawn even more to the rich and nuanced timelessness of classical music. My cats agree with me.