I can't speak for Harvard, but in the vast majority of the world, going to college is strictly on the basis of entrance exams, with some countries also using high school grades, nothing more.

This is done to avoid bias and/or favoritism. I am not an expert in U.S. admissions but my understanding is that they give points for things like whether your parents are alumni or have donated, whether you play sports, whether you were school "president" or other tests of popularity, and a host of things that in my opinion are pretty poor indicators of whether one should be admitted.