Among the many missing key controls, they don’t appear to control for college attended, so they are influenced by things like harsher grading at typical publics than privates. I’d expect SAT to be better correlated with applying to and attending more lenient grading privates, largely due to better correlation with income. Furthermore GPA was self reported and had limited granularity. For example, students could check the box for having an “A” HSGPA, but could not say their UW GPA was 3.43. Nearly every study that isn’t sponsored by the CollegeBoard shows much HSGPA is far more predictive of nearly any metric of college success than SAT scores. Some examples are below:
https://journals.sagepub.com/doi/full/10.1177/2332858416670601
10k Kids in CUNY System FY GPA
SAT explains 14% of variance in first year GPA
HS NYS Regents test explains 16% of variance in first year GPA
HS GPA explains 25% of variance in first year GPA
HS GPA + SAT explains 28% of variance in first year GPA
10k Kids in Kentucky Public Colleges FY GPA
SAT explains 16% of variance in first year GPA
HS KCCT test explains 17% of variance in first year GPA
HS GPA explains 32% of variance in first year GPA
HS GPA + SAT explains 34% of variance in first year GPA
https://files.eric.ed.gov/fulltext/ED502858.pdf
>50k Kids in UC System: 4 year graduation rate
SAT I explains 4% of variance in graduation rate
GPA explains 7% of variance in graduation rate
GPA + SAT I explains 8% of variance in graduation rate
>50k Kids in UC System: Cumulative GPA
SAT I explains 13.4% of variance in GPA
GPA explains 20.4% of variance in GPA
GPA + SAT I* explains 24.7% of variance in GPA
*Best prediction occurs with <=0 weight given to math SAT unless STEM major