Which is for the most part the entirety of a degree's usefulness beyond the first year or two of employment. It's a signal, and it allows a company to easily take a stack of 250 resumes for a single position and cut it down to 80 without a significant hit to the skill distribution. Some of the best are likely eliminated, but most of the worst are as well.

My sub-3.0 GPA for a humanities degree a decade ago has no bearing on my skill as a programmer, but it almost certainly means I won't be working for Google or Facebook.