At least with Engineering/Math/Hard Science you have to demonstrate via projects and tests that you have actually learned something.
That "something" is the ability to solve problems.
There is a simple formula: To be employable (in a free society) you need to solve more problems than you create.
Every employee creates problems - most notably they expected to be paid. Some individuals create additional problems by being high-drama, which makes them less employable, but that is another story.
If "getting an education" means the same as "learning to solve more and harder problems", then it is easy to see why getting an education leads to better employment prospects.
Much disappointment, bitterness, and argument ensues, methinks, when people confuse "earning a diploma" with "learning to solve problems". These are distinct things. Though there is a correlation between having a diploma and being able to solve a problem, the correlation is less than 1.0 and is quite a bit less, I believe, than most university administrators are willing to admit. This comes down to marketing: Universities do not sell problem solving skills, they sell diplomas, and so naturally they will emphasis the "earning a diploma" aspect over "learning to solve problems".
STEM courses are all the rage with employers now, I believe, because a STEM diploma has a much better correlation with problem solving skills than do other degrees. I do not think that is an inherent property of the STEM curriculum. My experience is that someone with a liberal arts degree can be just as good of a problem solver as someone with a STEM degree. I think instead that this is an indictment of the current horrid state of liberal arts education.
Note to students: If you desire is to be employable, focus on developing problem solving skills, not on getting a diploma. I don't mean to blow the diploma off completely - it might still be a technical requirement at the (unenlightened) HR departments of the companies for which you want to work. I mean instead that you should be constantly asking yourself "will this course improve my problem solving ability" rather than "will this course help me to graduate". I also mean that you should actively take it upon yourself to practice solving problems. And not just technical problems: business problems, interpersonal problems, societal problems, environmental problems, logistical problems - all kinds of problems. Do you see a piece of litter on the ground - pick it up and put it in the trash bin, and you've just solved a problem. Instead of being arrogant, bitter, angry, or hostile towards people you interact with, trying being kind and understanding, and you're on your way toward solving interpersonal problems. Make up your bed. Wash the dishes. Wash and fold your laundry. Make it your habit to solve common everyday kinds of problems like this and you are well on your way toward solving the bigger problems that employer are willing to hire you for.