[tricuspid]

Part of my intuition wants to buy into the idea that the age of exploration, and the sudden European expansion into the colonial/imperial territories of that period profoundly redirected the attention of people away from their peers, and instead toward the nature of the world at large (and maybe even humanity's place in the universe), and reduced the intensity of the run-away social chain reaction that produces interesting personalities that steal attention from each other.

If this analysis was only performed on English wikipedia, then there might be a degree of bias regarding European history. In any event, one would never expect the graph to bottom out, but possibly the reason the trough doesn't dip any lower than it does, could be that the rest of world history remains static, and picks up the slack, continuing to generate notable personalities in areas not disrupted by exploration.

Similarly, my intuition leans toward thinking that the long, steady, even duration of the trough might be an artifact of the nature of communication during the period, which also likely introduces a degree of delay between cause and effect. Long slow letter writing suddenly has to traverse an ocean or two, to maintain communication across populations spanning multiple continents.

https://en.wikipedia.org/wiki/Age_of_Exploration