They keep moving the goal posts

It's from 2009, but an entirely relevant read from Professor Jack Schneider on how we got AP tests and how they're leading to diminishing returns among lower income kids.

However, perception of AP had begun to change. The programme had expanded so rapidly at the end of the century that some colleges and universities, concerned with questions about the credibility of the programme, began to re-evaluate the practice of giving preference in the admissions process to those who completed AP coursework. Further, as of 2000, ‘the general level of selectivity and [criteria regarding] test scores’ among 4-year private universities, ‘were higher than they had been previously’ (Breland et al. 2002)—an indication that more students were exhibiting strong academic coursework and test performance than they had previously. Simply put, having AP on one’s transcript no longer provided the measure of distinction it once did.