Why do Ivys reject perfect candidates?

About the essay integrity issue - I have seen a lot of anecdotal evidence that colleges are well aware of the potential for abuse, and that they regard suspiciously well crafted essays as highly suspect and, at least in some cases, an automatic rejection.

Obviously, this is something that might unfairly impact a prodigiously talented writer as an applicant. Again, there is some unavoidable “luck” in the whole process.