Your analysis is overly dismissive of genres that you presumably don't like. Simplistic pop songs aren't a new phenomenon; they were just as present in the 60s as they are now. We just don't listen to them anymore as they haven't stood the test of time. This was abundantly evident last weekend when I went through a stack of about 100 45s from the 60s and early 70s that I inherited. (My father was a radio DJ during the time.) I'd never heard of 90% of the bands, despite already owning hundreds of albums from the period. The same will be true of the music that's popular now in a few decades.
Also, using harmonic progression alone as a measure of musical complexity or richness is misguided. Steve Reich's Violin Phase contains only 5 notes, but was a seminal piece of minimalist music in the 1960s:
Musical richness can come from a lot of places. Hip-hop, as a genre, tends to focus on rhythmic texture and narative content. I'd say, on average, pop hip-hop these days is richer than pop rock. There's also some really great stuff that's come out of the hip-hop world, depending on how far away from pop you're willing to still call something hip-hop, e.g. DJ Spooky:
(Note: Several members of The Roots are competent jazz musicians.)
Even Miles Davis's most known albums, Kind of Blue and E.S.P. represented a step towards more simplisitic harmony – "modal jazz" – far simpler than the hard-bop which was at the time prevalent and which Miles had previously played.
The assertation that harmonic complexity precluded the death of art music also seems off-base. Art music was always high-falutin' stuff that mostly rich people, or those wanting to emulate them, listened to. The rise of the relative importance of pop music had more to do with the invention of the phonograph than the increase in harmonic complexity. In fact, many of the first post-romantic composers, Satie, Debussy and Ives, tended towards more simplistic harmonies (arranged in ways that violated the rules of classical and romantic functionalism). It wasn't until the modern period, well after the rise of recorded pop music, that harmonies got particularly wild.
We just don't listen to them anymore as they haven't stood the test of time. This was abundantly evident last weekend when I went through a stack of about 100 45s from the 60s and early 70s [...] I'd never heard of 90% of the bands
There was a Cambrian explosion of music in that period, and virtually no one ever heard of 90%, probably 99%, of the bands. Countless groups sprang up all over the place and pressed records for their local markets. People have devoted careers to tracking down the recordings of that period; one of them, Greg Shaw (whom I knew for a while) had over a million records. He put out a series of influential compilation albums of his favorites that spawned an entire genre (garage rock). Decades later, this stuff is still being unearthed and released. There are entire series of albums devoted to the 1960s proto-punk of Oregon, or Denmark, or Uruguay. It's just amazing how much there is (enough that I'm skeptical of claims that more was recorded in the 80s), and much of it -- tastes vary, of course -- remains amazingly alive and good. A lot of people would disagree that it hasn't stood the test of time; every generation produces new acts in this lineage (e.g. Black Keys), and the underground history of the music continues to be handed down through the fanbase. Its popularity ebbs and flows in a 10-year cycle or so. Right now it's on an upswing.
Edit (by way of response to the rest of this thread, not to your comment): it's foolish to identify complexity with good music. Punk/new wave was a reaction against complicated, highly produced music which used an awful lot of chords. The entire career of bands like the Stooges and the Ramones was a self-conscious mining of the opposite aesthetic. Consider the famous 2-note guitar solo in the Buzzcocks' "Boredom": http://www.youtube.com/watch?v=QoYiQ8Qsozk&t=1m19s. The rest of the band was rolling on the studio floor laughing while the guitarist played it because nobody believed it was possible to do a guitar solo like that, let alone for that long. It's as far from complicated as you can get but still a great creation. Or think of John Cale's one-note piano drone that runs through the Stooges' "I Wanna Be Your Dog": https://www.youtube.com/watch?v=3gsWt7ey6bo#t=23. Cale came from La Monte Young and the Fluxus movement -- highly self-aware avant garde early 60s stuff that he put into a deliberately primitive incarnation. Not saying everyone should like it, but it's as influential and artistic as anything of the last 40 years.
The only rule is that you can't predict what form great art will take. The minute somebody thinks they've figured it out (number of chords? please), the muses jump and bless the opposite.
> There was a Cambrian explosion of music in that period
This is a bit of a simplistic explanation. Underlying this its really just that recording, playing and distributing music at reasonable quality became much cheaper and easier, so we rapidly went from a world where music was incredibly localised and diverse but not an attractive career (because nobody made much money) to one where music was heavily internationalised and less diverse, but more attractive as a career (if you could 'make it').
Sorry if you think thats a nitpick, but I really don't see any evidence that the music of the 1960s was an 'explosion' (in diversity? i assume is what you mean) from what had gone before, just more recorded (probably some good stuff, but also a lot of trash - because suddely you could dream of making money from it).
Come to think of it, "Cambrian" isn't the best qualifer since there wasn't an explosion of species (genres), but of records in a few popular genres. Let's just say "explosion".
This didn't happen just because music was "cheaper and easier". It happened because of the youth culture of the 60s and the asteroidal impact of rock and roll (better science metaphor?), especially the British Invasion of 1963-64. Kids started bands because it was cool. Most weren't expecting to make money or become stars. They were in it to imitate their heroes and impress girls. This history is well known to fans and students of the period, and it's documented. Fanatical pop archivists have traveled to places like Kansas City and tracked down members of bands who pressed 300 copies of some 45 they recorded in 1966 and interviewed them about it.
By 1969, there was a sharp dropoff, not because the economics changed (it's not as if electric guitars got more expensive) but because the cultural moment had passed. Rock and roll became "rock" and started taking itself seriously. Bands started putting out slicker stuff that, in retrospect, was far less fresh and exciting. Fans of rock and roll talk about those years as the dark ages. The DIY aesthetic kicks back in bigtime with punk, which was a conscious effort to revive the values of the mid-60s (https://www.youtube.com/watch?v=UHPQI4b0ybE#t=18).
As I said, this stuff is all well documented. I learned about it from old fanzines and liner notes, so I don't have websites handy, but it ought to be pretty easy to find out about.
"Consider the famous 2-note guitar solo in the Buzzcocks' "Boredom": http://www.youtube.com/watch?v=QoYiQ8Qsozk&t=1m15s. The rest of the band was rolling on the studio floor laughing while the guitarist played it because nobody believed it was possible to do a guitar solo that insane, let alone stick with it for that long. It's as far from complicated as you can get but still a great creation."
If he hadn't spent twenty seconds hammering out E-B-E-B, the ending Bb wouldn't be special at all!
Also, using harmonic progression alone as a measure of musical complexity or richness is misguided. Steve Reich's Violin Phase contains only 5 notes, but was a seminal piece of minimalist music in the 1960s:
http://grooveshark.com/#!/s/Violin+Phase/3nPoC4?src=5
Musical richness can come from a lot of places. Hip-hop, as a genre, tends to focus on rhythmic texture and narative content. I'd say, on average, pop hip-hop these days is richer than pop rock. There's also some really great stuff that's come out of the hip-hop world, depending on how far away from pop you're willing to still call something hip-hop, e.g. DJ Spooky:
http://grooveshark.com/#!/s/Peace+In+Zaire/2UyeL0?src=5
Just as an example, I love the texture of a lot of stuff from The Roots:
http://grooveshark.com/#!/s/Don+t+Feel+Right/2LzmSC?src=5
(Note: Several members of The Roots are competent jazz musicians.)
Even Miles Davis's most known albums, Kind of Blue and E.S.P. represented a step towards more simplisitic harmony – "modal jazz" – far simpler than the hard-bop which was at the time prevalent and which Miles had previously played.
The assertation that harmonic complexity precluded the death of art music also seems off-base. Art music was always high-falutin' stuff that mostly rich people, or those wanting to emulate them, listened to. The rise of the relative importance of pop music had more to do with the invention of the phonograph than the increase in harmonic complexity. In fact, many of the first post-romantic composers, Satie, Debussy and Ives, tended towards more simplistic harmonies (arranged in ways that violated the rules of classical and romantic functionalism). It wasn't until the modern period, well after the rise of recorded pop music, that harmonies got particularly wild.