It may be helpful if you view the selection process from the perspective of the school admissions officers. Their goal–at the most selective schools–is to build a class.
Building a class means that many needs & wants of any particular school need to be satisfied. Schools need males & females of different races/ethnicity from different geographical regions and seek socio-econmic diversity. Schools need athletes, musicians, scholars, dancers, artists, writers, math & science whizzes and students with a variety of academic & social interests.
The most elite schools attract the top students in terms of academic achievement & in terms of stats (high GPAs & high standardized test scores).
Additionally, the process is a bit clouded because there are no set qualifying standards that one has to meet in order to apply to any particular group of schools. And there is no limit as to how many schools to which one may apply.
While many foreign school systems prioritze verified academic achievements, US colleges & universities strive for diversity in all of its forms, and seek “entertainers” as well (athletes, musicians, dancers, actors, & writers).
Diversity brings more varied perspectives to campus. Students live together, learn together, and learn from each other both in & out of the classroom.
Sometimes admission is determined by a single need such as for classics majors, a quarterback on the football team, or members for the marching band, school orchestra, dance troupe, or journalists to write for the student paper. Leadership is a prized attribute as is documented success in research or in community service.
In short, US colleges & universities create/build communities based on much more than academics.