Unlike universities in most (all?) of the rest of the world, academic studies & grades are intentionally not the only mission within US schools. Extracurricula

Unlike universities in most (all?) of the rest of the world, academic studies & grades are intentionally not the only mission within US schools. Extracurriculars, social clubs & sports are hugely important, to the point that selecting for "well rounded" success is something colleges try to do. As others have stated, if it was based purely on grades it would be almost random. Grades are too easy to fake or inflate, and many high school students just coast through with straight As, whether they actually have a special aptitude for academics or not.