It is also the result of deliberate policy decisions to favor HS GPA more than SAT/ACT scores within the realm of academic criteria in admissions. This is the result of (a) its own research suggesting the HS GPA is significantly better predictor of college GPA than SAT/ACT scores, and (b) its holding to the mission of offering opportunity widely within the state population, including to those from low SES backgrounds (SAT/ACT scores correlate fairly strongly to SES). So, for the USNWR criteria, the UCs should do well for the percentage of students in the top 10% (largely correlated to HS GPA, even though HS class rank is not explicitly used), but less well in SAT/ACT scores.
It also means that applicants who are heavier in one or the other of HS GPA and SAT/ACT scores may see differing results among schools which, at first glance, appear to be selectivity peers. For example, UCLA and USC are typically seen as selectivity peers. But UCLA favors HS GPA, while USC favors SAT/ACT scores (this is noticeable when looking at each school’s frosh profile from their own web sites), so that a HS GPA heavy applicant has a better chance at UCLA, while an SAT/ACT score heavy applicant has a better chance at USC.