Also, one reason some jobs prefer applicants with degrees is because university completion shows that you have some ambition and willingness to work hard toward a goal that is several years away, in the face of deadlines and stress, and possibly financial risk also. They know you've pulled a few all-nighters to get through.
In other words, you're gone through a pretty tough four year (or more) project: to produce a degreed version of yourself.
That degree shows that you can work, even if you don't have employment experience.
Yeah you are probably right about ambition as a general filter too. But the point remains that universities take advantage of this. They know full-well that plenty of students are there to get a job and they can and do milk this.
Issuing degrees is not part of Universities being "about education". Degrees are an arbitrary milestone, that can be received after completing a nearly arbitrary set of classes, that in-turn have taught an arbitrary set of lessons. The fact that Universities have coalesced around issuing degrees of the same type without ensuring their curriculums match further makes the degrees aribitrary.