'Black box' doesn't mean 'numbers in a computer', it means 'nobody can explain to me precisely why I was rejected'. A score calculated from an obvious formula is fine (regulations permitting) since you (or a regulator or court or the institution) can establish precisely why you were rejected. A black box system is one in which this cannot be established by any person.

This is obviously bad for both legal and moral reasons. Legally you may be (unintentionally) violating anti-discrimination laws. Morally you may be setting up a system that arbitrarily denies people who are otherwise deserving with little to no recourse.