I feel very difficult exams should be commonplace. Everyone should be held to very high standards. It's surprising how many professions don't do this. For example, I've been to several physical therapists who barely seemed to understand what was wrong with me even after several visits. Each gave me what seemed like the same standard routine that they give everyone with problem.
Meanwhile, they often gate the requirements to even take the test. It would be chaos (and bad for the law schools) if someone were able to take the bar without a JD (some states have just as lengthy apprenticeship periods replace that) or otherwise prove professional ability acquired via non traditional means.
I was somewhat surprised watching the Perry Mason series on HBO last year when Perry Mason was sworn to the bar without actually going to any sort of law school. Apparently that was the norm until after World War II.