I emailed BU for app feedback after the R and they had some pertinent information about this in their response (I've cut out the places where they gave me specific feedback):
"I would like to help you understand our decision on your application but I fear that I will, inevitably, disappoint you. In a comprehensive, holistic review process like the one we use in our Admissions program, there is rarely a “smoking gun” that knocks an applicant out of contention. That is, we almost never find a single factor in the applicant portfolio that forces us to decline the candidate.
Our decisions are, inevitably, made in the context of a very large and well prepared applicant pool. Specifically, we anticipate receiving more than 9000 applications this cycle, and of these the vast majority are from applicants who are well-qualified for the study and practice of medicine. Since we have capacity to interview only about 1000 candidates in the course of a single admissions cycle, we will be forced to eliminate more than 85% of those qualified applicants without ever meeting them in a face-to-face interview.
We find this to be extremely challenging and often downright sad. We recognize that our decisions are subjective, but we do read every page of every file and do the best we can with the information available to us. I have no doubt that we make mistakes and that we turn away many terrific candidates, some of whom would have been a great match for our school."