The age-graded system is a dehumanizing legacy of the industrial revolution. It has nothing to do with teaching people how to think but was purposed to shoehorn people into "productive" career paths. "Liberal arts" education today is structurally flawed in such a way that people only receive incoherent bits of information without ever learning to think cohesively. So you end up going to class and learning to recite M…
And if I were an employer, it would make it much harder to determine who to interview. If you remove "dehumanizing" numbers like grades and test scores from resumes, how does Google (for example) know whether to interview you, who had a 3.8 CS GPA and a 1550 SAT, over the guy who slept through class, turned in code that didn't compile, and can't explain the difference between = and == (yes, I knew people like this as an undergrad)?
That said, this is all from the perspective of an engineering student. I suppose it's much harder to quantify performance for the liberal arts (which is probably part of what initially pushed me towards engineering, now that I think about it).