It comes down to this: filtering by OSS contributions gives you many false negatives (as the OP has complained) but virtually zero false positives. In hiring, a false negative is a bummer, but a false positive is disastrous. It would be irresponsible of me as an interviewer not to take this into account.
If it someone's pissed because they fall into the false negative bucket, that's rough, but I'm the one calling the shots and taking the risks.