For whatever reason, anecdotes resonate better with most readers than just pure data. So even articles that are really about the data will often include an anecdote to keep readers interested.
Of course, the fact that anecdotes resonate better than data also means that one outlier anecdote is more believable to many people than all of the data that shows that the anecdote is an outlier.
As far as the predictive power of HS GPA and SAT scores, both UC and Harvard have noted that HS GPA is more predictive of college performance than SAT scores. Both also found that achievement tests (SAT subject and (for Harvard) AP) were more predictive than SAT scores. But the achievement tests are the non-default tests that many students do not hear about until too late, so colleges may be reluctant to require them for that reason.