One possible answer to that question, presumably not the one you're thinking of, is that those jobs are largely mechanical and require less creativity or generalized problem-solving ability than software engineering.
Edit: I don't mean to suggest that I think these kinds of questions are good for hiring software engineers, just that your argument for why that isn't the case may have some holes in it.
Edit: I don't mean to suggest that I think these kinds of questions are good for hiring software engineers, just that your argument for why that isn't the case may have some holes in it.