The death of the key change
My hypothesis is that you can choose any aspect of composition that musicians find exciting and note the same decline over time. You don't have to be a music theorist to observe that by and large, today's music has been dumbed down in comparison. On a scale from "most producer friendly" to "art" it's definitely leaning heavily to the left.You can especially note that when it comes to harmonies, and harmonic shifts (aka key changes) are not the only aspect that has been greatly simplified. Elaborate harmonies are just not a thing anymore.And that's not just the typical effect that old generations cannot relate as much to the music of new generations. No, it's that today's taste - which, of course, has been mostly shaped by the exposure to today's music - appreciates songs that are, from a musician's perspective, much simpler in almost every aspect. The only exception that I can think of is that the performance capabilities of the singer have been put much more in the focus, so you can find songs today that are really difficult to sing well. This is mostly true for female performers, though, and the beginnings of that trend can probably be traced back to Whitney Houston and especially Mariah Carey, who made a certain Coloratura-style of singing fashionable.I think hardly anyone will dispute the observation that today's music business is much more professionalized than it had already been since the beginning of recording technology. And that goes to tell. It really _is_ a business, and the process of producing a hit song has been streamlined tremendously.Of course, we need to keep in mind that the focus of the article (as well as my comment) is on chart pop music. And of course, this is a big-picture kind of observation, not claiming that you couldn't cite some (however, rare) exceptions here and there. A thriving alternative scene with much more elaborate song writing has never ceased to exist, but that's not what gets played on your average top-40 radio station (for the youngens: "streams").