I would suggest two things. First, you have seriously underestimated the variation among secondary educational institutions in USA, a mistake that no USA college admissions process would make. Second, even in the context of the fortunate realm in which you attend university, a "good grades guarantee acceptance" policy probably somewhat underestimates the variation among secondary educational institutions there.
Probably because the country I live in has much less variation in the quality of secondary education.
The fact the US hasn't figured out how to offer a consistent level of K-12 education is, quite frankly, mind-boggling (along with the lack of health care, and many other things we take for granted in the rest of the 'western' world).
