They have to - it’s likely they have far more applicants with near perfect GPA/Test score combos then they have spots. (Noting that your GPA gets fuzzy once it’s over a 4.0 since that “extra” is going to be somewhat school and school system dependent)
Since each kid likely applies to multiple schools the process would also be extremely broken if it worked the way you suggest since the same cohort of kids would all be accepted to multiple schools and the schools would then have to backfill from a alternate list - which would also be the same cohort of kids…