Either something like this is being up collected and articulated up through the decision points in the hiring process, or the decisions are being made on a fuzzy basis that can't even be explained internally, which presumably represents a risk that decisions couldn't be properly justified should a candidate suspect discrimination and pursue a claim.

(This is especially true for any kind of exercises, btw. If an employer asks me to do some, I am going to screen them on whether they have (a) complete reference solutions with (b) numbers on how long it took to complete each and why they're confident those numbers are reliable(c) a written rubric for evaluating candidate solutions that (d) they'll agree to share with me when we're done.)