Explanation of co-occurrence from the abstract of a Woodley paper:
It has been theorized that declines in general intelligence (g) due to genetic selection stemming from the inverse association between completed fertility and IQ and the Flynn effect co-occur, with the effects of the latter being concentrated on less heritable non-g sources of intelligence variance. Evidence for this comes from the observation that 19th century populations were more intellectually productive, and also exhibited faster simple reaction times than modern ones, suggesting greater information-processing ability and therefore higher g.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4404736/
IQ is to g as basketball skill is to height: https://www.unz.com/isteve/nba-players-are-getting-shorter/
“You can’t teach height” – Red Auerbach
“NBA point guards are 6’3’’ tall, tallest they’ve ever been.”
“All other positions (shooting guards, small forwards, power forwards, and centers) are the shortest since the early 80s.”
So where before you’d have absolute genetic monsters like John von Neumann and Wilt Chamberlain effortlessly dunking on their competition for 100 points in a single game, now you have extremely conscientious technicians like Steph Curry shooting from the hip at half-court for 12 hours per day (Curry is also an accomplished amateur golfer aside from being an NBA superstar, which requires a similar type of deliberate practice).
The really interesting thing is that the inflection points in average NBA height, average general population height, and the Flynn effect on IQ scores all happened at exactly the same time: y2k.
If you’re into this kind of thing I’d recommend the entire article for concept porn. E.g. K-selection is turning us into the Finns:
“So it’s not strange that 61% of the NBA players are within 6 inches, standing between 6’3’’ and 6’9’’. All other height ranges are in decline.”
Aeoli Pera 
Y2k is roughly when advanced analytics came to pro sports (see: Moneyball). Basketball execs figured out that close shots are actually very inefficient unless the 3-pt. percentage drops below a certain number, which was surpassed in the late 90s as those players grew up shooting threes and older players did not. Premiums on tall guys went down unless they could also shoot, which they do in Europe, which is why all the seven-footers now are from Lithuania. Point guards went from being pass-first to shooters, so they needed a little more height. The result is space the floor, be quick and shoot a lot. Don’t need much height to do that.
Similarly, all the money is in one-to-n micro-innovations. High-g, zero-to-one macro-innovation is a great way to be poor.