I've started looking more systematically into whether cover songs choose original versions that were from a matching phase of the 15-year cultural excitement cycle. Probably won't have the full results and discussion for a few days.
But I did notice something striking so far -- there hasn't been a single cover song to make the year-end charts since 2006 ("Life Is a Highway"). That ends a tradition of cover songs being popular.
Even more bizarrely, this is the same period during which all hit TV shows and movies have become remakes, reboots, and other derivative forms.
What's the difference?
Songs are lyrical and more personally tied to their creators, whereas narratives are more impersonal and only loosely tied to their creators (except where the narrative is considered the distinctive work of an auteur).
Songs are also more tightly defined formally -- by their melody and lyrics, whose alterations turn it into a different song. Narratives are more loosely defined, with an overarching plot, themes, and character types, which can be altered somewhat without turning it into an entirely different story.
So, covering a song commits you more to the efforts of someone else, and is less of a showcase of your individuality. Remaking a movie requires less faithful of a commitment, and allows more individuality to show.
Whether the void of original ideas during the 21st century, and the rise of individuality since roughly 1980, is due to the production or consumption side does not matter here. The point is that, although the culture overall seems bereft of new ideas among producers, and/or uninterested in them at the mass audience level, the two types of media are reacting in opposite ways to the same trends.
In both of them, the makers want to showcase their individual awesomeness, despite a lack of originality. Movie makers can dress up someone else's child in their own individual styling and pass it off as their own creation, while songwriters cannot because everyone has such a narrowly defined expectation of what that other person's child is supposed to be like.