I'd like to start giving people the option of commenting on shorter Cold Takes pieces (which I don't cross-post here or provide audio for). I'm going to use this post for that: I will generally leave a comment for each piece, and people can leave their comments as replies to that.
You've done an admirable job of charting the relative "quality" of intellectual/artistic/musical advances but not the "why" other than, "it was cool to be smart" as in ancient Greece. What other factors could be considered? Let's start with nutritional—did the consumption of stimulants like caffeine and later, tobacco, bump up the advances? Did the consumption of large amounts of alcohol, served in pewter, serve to depress IQs enough to perpetuate the Dark Ages? Did recreational drug use boost the creativity of music and art in the mid- to late-20th century?
Then there are political/military factors, such as the burning of the library on Alexandria or (for instance) the clamp the Chinese dynasties held on technology and trade. When the Europeans first visited China and learned about gunpowder, they took the tech and improved on it. When they returned centuries later, they had improved their cannons while the Chinese were still using the same designs from earlier.