I think what you're missing is the shear number of candidates. Does requiring (or even weighting at all) academics result in false negatives, absolutely. However candidates with a CS degree tend to, on average, perform better and there's a lot less of them when compared to "total population looking for a job". This makes filtering on a degree a cheap and effective signal when you aren't dedicated to having technology people do nothing but interview all day and everyday to find talent without hefty prepruning.