The hiring manager needs you to do that for typical corporate CYA reasons. If you turn out to be a great hire, it's all good. But if not, then the hiring manage

The hiring manager needs you to do that for typical corporate CYA reasons. If you turn out to be a great hire, it's all good. But if not, then the hiring manager can say, "he was top 10% (or 5%, or 1%) at HackerRank, blame it on them", as opposed to, "I incorrectly evaluated his competency/fit/experience/motivation/etc." It's for the manager to have someone to point a finger at, if necessary. Simple as that. Some HR depts may have instituted the policy, same thing just larger scope.