Some thoughts:

* Inflation of people with college degrees. From 5% in 1940 to 35% in 2019. This dilutes the quality of both the student pool and of the professorial pool.

* Distance from the last major war, all the way back in 1945. Educate like your life depends on it has long faded from memory. In medicine, in engineering, in hard sciences.

* The mismatch between skills taught in academia and job market skills. By now everyone is jaded at the notion that the main point of education is the diploma, seen as a key to unlock the job market. Of second importance, networking, get into an Ivy to rub elbows with the right crowd. Knowledge and critical thinking come as a distant last.

* Or perhaps, even simpler, the dilution of the male spirit which sees competitiveness in excellence as an inherent moral good. Our forebears wore educational attainment as a peacock plumage. These days peacocks are outright vilified.

What do you mean by quality here? I'd say the quality of the teaching has been going up as the quality of the students has been going down (precisely because access is going up). The focus is increasingly on the lowest common denominator which requires a lot more effort from teachers.

I imagine the situation is country-specific and I’m not aware of any good studies that try to measure it. But anecdotally, as a university student around 2010, I noticed that the standards expected of undergraduates in old textbooks, exam papers and theses seemed higher. Maybe it’s just that these sources gave me the false impression of an ideal student, but a lot has changed in recent decades. As well as the growth in the student population, by 2010 it was pretty common for “full-time” students to work part-time as well.

Hannah Arendt was probably an exceptional professor in 1955, but I wonder how this compares to a final exam for a first-year political science class at an exceptionally good university today? https://twitter.com/Samantharhill/status/1297545059466907650