testing, testing, 1-2-3

Here is what I don't understand about advanced degrees. Why do we go through years and years of school, learn all sorts of things about that particular career, get tested on those things, but then still have to take a whole separate test in order to prove that we should be allowed to engage in that profession? In my case, I have spent years and years investing in my education. I go to school, I study, and then I'm tested on the things that I've studied. And yet, after all of this, I still have to take two other big tests (one of which I will be taking this weekend) to prove that I should be allowed to practice law. Why can't the state bar be in charge of deciding what is taught in law schools and administering the exams for those subjects? That way, if you graduated from a law school in the State of Moot, then you would be allowed to practice law within the state of Moot. If you later decide that you want to practice law in a different state, you would then take a test for that particular state since you didn't go to a law school that specifically taught the laws of that state.