I worked in construction and electronics. Morons were not valued in those fields, either.
But it doesn't take a genius to be a great plumber, electrician, framer, pipe fitter, machine tool maker etc. Smarts are required to solve problems that haven't been experienced before. Many jobs have the solutions already worked out in fine detail or are learned as an apprentice. Then it only requires knowledge of the solution (or where to go get the knowledge for the solution), a good work ethic and a desire to do the job right.