Bearing in mind the relatively large number of people that simply weren't the right demographic or lacked the earlier education or money to pursue a PHd in 1900

Bearing in mind the relatively large number of people that simply weren't the right demographic or lacked the earlier education or money to pursue a PHd in 1900 irrespective of their aptitude, you'd expect that per capita number to massively increase even before we get into universities' incentives to enroll more students That of course can lead to both 1 and 2 (why not both, and let's not forget that smart high school kids today know things which the very best of the PhD candidates hadn't done the work of figuring out yet in 1900)