For one, when they graduated in the early 60s there was a massive gender gap in college attendance - my mom was valedictorian and went to secretarial school because her parents told her "women can be teachers, secretaries, or nurses", by the 70s she knew she should have gone to college. For comparison the female valedictorian from my HS went to Harvard.
Then there is the general quality of the education. Neither of them took Calculus in high school. They had Latin and most schools today teach Spanish, French, and Italian but aside from that they think my education was much harder. College is unquestionably more rigorous today.
On a shorter time frame, say the last 10 years, MAYBE that argument holds true. In my home state the last 3 have had serious state budget problems that affected the schools but until then it was getting better and better every year.