Right, pop comes from a tradition that started with African polyrhythms and went through spirituals, ragtime, blues, jazz, rock, motown, punk, R&B, metal, rap, etc. I don't know the detailed history of all of this, but I do know that 50's-era rock was very simple, much simpler than the jazz and blues from which it evolved. Rock subsequently expanded into something more complex by around the 70's and early 80's, after which I think we saw simplification again.
Usually the "new, edgy" styles are simpler as a rebellion against the complexity that existed at the time. Look at the beginnings of punk, for example (or of 50's rock).
I don't feel like modern pop music is driven by a rebellion against any musical tradition, though. To me it feels like we've had about two decades of "blah". I also get the impression that young people of today (my generation and the two or three after), in this country, don't feel very strongly about anything in particular, musically or politically. Where previous generations saw musical movements, today we seem to have musical complacency. It is mere entertainment, and not a "voice". There are probably several causes.