Slides and nested bullet points are a very efficient way to organize and present ideas. Students clearly prefer bullet-point summaries to paragraphs. All professional slides use bullet points. So: why did it take humanity so long to invent the nested-bullet-point structure?

One possibility: bullet points take up a lot of space. If paper is expensive, you want to maximally use the space, which leads to paragraph-like structures. Did we inefficiently write in long bloated paragraphs, simply because paper was too expensive in the past?