It depends I suppose on how you define “book series”. If human development had somehow skipped capitalism and gone straight to something more like what we’d think of as industrialized socialism, there would probably be less individualized fiction book series written by a single author.

But if we define book series as simply a continuation of storytelling within the same universe, fiction or nonfiction, I don’t see how society would ever not have that. Before writing, a lot of history got passed down orally I’m pretty sure. In order to have an oral history, you would have had to be memorizing and passing down a lot of important stories about what came before. These may not be series in the sense of strictly chronological series of events with a clean beginning and ending, but they are still expansive storytelling, as opposed to one-off one-and-done stories.

If anything, I’m inclined to argue that one-off narratives are the more abnormal thing. That it is more normal in human history for narratives to be about the same “world”, usually a nonfiction one. From a logistical standpoint, even in the context of fiction, this is just easier to do; the main force opposing it is intellectual property rights, but fan fiction sometimes bypasses this anyway and gets away with it because it’s not competing for money / claiming to be official works. Making seemingly “original” works is kind of overblown as valuable and harder than it sounds, and some of the works that are perceived as original were inspired heavily by works that came before them. I can’t remember the details off the top of my head, but I’m pretty sure Star Wars was inspired by movies before it (maybe WWII stuff?). I know some of the music took intentional inspiration from Gustav Holst’s The Planets (and he surely took inspiration from things from his era).

So originality is a bit of a myth, depending on how you look at it.