It's pretty generally acknowledged that grade inflation began during the Vietnam war, particularly at liberal schools where many professors would not give failing grades that might subject male students to the draft.
And the late '60s and early '70s saw the beginning of widespread affirmative action admissions. And since it was so vital to have diversity in admissions, it became equally vital to have diversity in graduation.
And since, all sorts of games have been and are played to justify affirmative action in college admissions, grad school and professional school admissions, and in hiring and in Congress (gerrymandering).
Standards have been lowered in most every aspect of education until fashioning the desired outcomes is more important than quality education.