I have no idea how people here manage to infer what other's think or feel when there is nothing to indicate those thoughts or feelings in their posts. The OP didn't seem able to differentiate between acquiring knowledge or skills, which can be done for little or no cost, and acquiring a degree formally acknowledging that you've acquired knowledge or skills which unfortunately costs a pile of money here. Hence the answer to the question posed in the OP's title becomes "because it costs that much, or a ton more, to get a degree no matter how much you know." What makes me seem "proud" of that?
Do I agree with you that a person should be able to pass some free or very cheap tests proving they've acquired knowledge or a set of skills? Yes. But we don't have that option and even in situations where passing a test is required to allow someone to do a kind of work, e.g., law or medicine, you generally are not allowed to sit for those tests without a degree. So again, that's why people pay a lot of money for a degree that they may not need in some idealized place but in reality they do need.
As an aside, I personally do think there is a lot of value in acquiring higher degrees even if they don't translate to a cushy job with a fat paycheck but think the cost of some of those degrees is outrageous.