The notion of good pedigree benefits anyone who might fit in that category, so they're incentivized to convince people that this matters. For example, if someone on a hiring committee sees an applicant coming from their alma mater, they can call that a "good pedigree" and reinforce the value of their own background.
There's also a lot of discussion here around the people who get excluded because they lack that pedigree. I don't think anyone is saying that you can't find brilliant folks who went to a small school you've never heard of. They're saying that you're hiring for one professorship, there are a lot of unknowns, and you're trying to eliminate false positives to avoid a bad hire. Seeing that between two otherwise-identical candidates, one of whom has a BA from Harvard and one of whom has a BA from West Virginia State, you're well within your duty as a member of the hiring committee to assume that the person from Harvard has at least as good a chance of being acceptable as the other one. False negatives are okay (not great), false positives are horrible.
So statistically it is actually far more likely that the Harvard person is relatively mediocre to a neutral sampling of the entire system.