Why do people need a law degree in order to take the bar exam?

why do people need a law degree to take the bar exam? why can't you simply take the exam and if you pass you become an atty? I've litigated for over 20 years with several wins...some big, some little, and very very few losses. I have no degree and no formal education. I have worked as a law clerk for a law firm, I have worked as an independent legal contractor for firms in ohio, indiana, new york and I think minnesota. I am entirely against having to produce a piece of paper indicating that I know my stuff when my lawsuits and the judgments therein are clear proof I know my stuff. To me, this is a silly procedure designed to give attys this 'air' of "Im a smart person and i got a piece of paper to prove it" when i think that your abilities should be based upon your performance.