In general, hiring practices probably optimize for filtering out bad (or at least somewhat speculative) hires over passing on a potentially really good candidate (especially if there are any concerns to go along with the overall positives).

Of course, if the pipeline is massive (whether it's jobs, schools, etc.) this tendency gets amped up even more and anyone who doesn't come across as pretty much perfect on all dimensions--whether they are or not--is going to get dinged.