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.
At the beginning of my senior year in college, I sent them a resume containing my GPA (3.9/4.0) at a public school (Clemson).
I heard back from Google within a couple weeks, had a few phone interviews, and then they flew me out for an on-site interview.
I had friends with similar credentials, but lower GPAs (< 3.5/4.0) that never heard back from Google.
Having a degree or high GPA doesn't matter to them once you're interviewing, but its tough to even get an interview without one.