At 6 a.m. every weekday, a group of sturdy-framed men in steel-toed boots clock into the small factory at Quaker City Castings to build sand molds, pour molten metal and grind iron and steel castings. The jobs are tiring, feature hazards not found at desk jobs and are tough to fill. Once workers are recruited, it can be difficult to get them to stay. This is work politicians lionize, but Americans often don’t want. “A lot of people say they wouldn’t work in a place like this because of...