This is what I tell my two daughters who have both opted to not attend university immediately after high school:
To an employer, a college degree conveys the fact that you are capable of setting a multi-year goal and actually achieve it.
While this seems trivial, it is remarkable how many people think they CAN do this, but when put to the test, cannot.
Aside from very low-skill specialized jobs at the lower end of the labor pool, employers need people who may not necessarily or likely already possess all the prerequisite skills at the time of hiring, but can set and achieve long-term goals, especially those with externally/extrinsically defined requirements, such as graduation requirements, or job requirements.
Can you get a job without such proof? Sure. But, will having proof help validate your claim that you possess the skill? Absolutely. And, despite what many think, there are plenty of people who do not possess the skill, and those people cost employers in both time, money and other resources, so employers look for ways to mitigate the risk of hiring them.