I have a relative who is a boilermaker, though now he supervises. Listening to his stories, there's never any shortage of idiots. A good team requires some veterans and some good supervisors, all whom need to constantly keep an eye on the idiots, lest they kill or maim themselves or someone else. Also, AFAIU, there are often rules requiring a minimum percentage of local union members on a project. So the number of idiots on a project is both a function of the quality of the local membership, as well as how many reliable veterans the national union and contractor can put on a project, assuming a project will even have non-local union members.

While much less physically exhausting, he doesn't much like his new job supervising, which entails alot of walking around and exclaiming, "WTF!?"