Most licenses mean that you know how to fill out a form and wind your way through bureaucracy.

I have taken tests from people who had no clue about the test they were giving.
I have been to building departments where i had to educate the plan checkers.

Proving competence would be great, but when you know that most must pass, the bar is set so low that it doesn't keep the incompetent out, just the unlucky who showed up on the wrong day.