Why were ethnicity and gender key determinants in how jobs were allocated in late nineteenth century industry?

In the late nineteenth century, rural Americans, although highly mobile and frequently city-bound, mostly rejected factory work. They lacked the industrial skills for the higher-paid jobs as rollers, molders, and machinists, but they did have skills - language, basic literacy, a cultural ease - that made them employable in the multiplying white-collar jobs in offices and retail stores. So the United States could not rely primarily on its own people for a supply of factory workers, except in the South. The textile mills that sprouted in the Carolinas and Georgia recruited workers from the surrounding hill farms, where people struggled to make ends meet. Paying rock-bottom wages, the new mills had a competitive advantage of as much as 40 percent lower labor costs over the long-established New England industry.