Well, I can't speak for other programs/fields, but it's probably similar. Would you trust me to be your pharmacist, if I say...just left high school? What about if I've been training with the local chemist for the past 4 years, so that the amount of learning time is the same as a uni course? What's the difference?

Difference is that a University, as the name suggests, is a collaboration of experts from many fields. If I stayed at the drug store down the road, I'd be learning, yes, but only what the pharmacist knows and is able to teach me. There is no guarantee of standard nor accuracy which is being passed on.

At a university, everything is peer reviewed and the knowledge is coming from those actively researching in your particular area of interest. I don't know how easy or hard it is to pass other subjects, but here, you really have to study consistently to pass. Bludging then cramming can work, but you'll have to have some uber capacity to pull it off. As you go further into your studies, it builds more and more on your previous knowledge, so it's not like you can memorise and forget.

In the end, I think places like university, colleges and other tertiary education institutions are places where they train qualified people in a selected area. It's not an intelligence filter. The cut-offs are there to limit supply/demand in a way deemed fair by the academic society and to a lesser extent, give an idea of the difficulty of the course.