Companies tend to put an emphasis on avoiding false positives, and usually don't care much about the risk of false negatives. They know it's possible for someone to be great without a degree, or any other random arbitrary requirement. But they know that there's a higher likelihood that someone without the requirement does not fit what they're looking for, so they're willing to lose desirable candidates as long as it removes a certain ratio of undesirable candidates.

This is specially true of companies that get thousands of resume submissions, like Google, Facebook, etc. For them, removing the noise is a huge challenge.