I think part of the problem is financial. The job doesn’t pay enough an hour, and the government benefits are too high.
That double whammy means smart people—who are fewer and fewer today—seek better paying jobs, middle intelligence people go on welfare while scamming an easy to scam system, and the drugged and dumb seek manufacturing or broom pushing work.
Meanwhile, illegals work their tails off in agriculture, construction and service jobs, and further squeeze the stupid into crappy jobs.
Construction jobs are not, necessarily, occupied by “stupid” people.