My understanding is the particular area had a long history of unionization, maybe particularly by African Americans.
I read about it elsewhere, but here's the first source I could find that speaks to that:
https://www.brookings.edu/blog/the-avenue/2021/03/16/the-ama...
> In the South, anti-labor laws are inextricably linked to the historic suppression of Black workers. Racism in the form of no- or low-wage Black labor has been part of the growth model of racialized capitalism. And when workers are unable to collectively bargain and demand their fair share, economic growth becomes concentrated in the hands of a few.
> Fortunately, the Birmingham metropolitan area—home to Bessemer—has already proven that unionized Black workers can create economic growth and shared prosperity. At the turn of the 20th century, Birmingham labor unions facilitated the establishment of a Black middle class. Black and white miners organized to form the United Mine Workers (UMW) union and, together, secured better wages. Following UMW’s success, what was then known as the Alabama Federation of Labor (AFL) followed the same strategy of a racially integrated membership—in part out of fear that nonunionized Black workers would replace striking workers. As a result, Black Alabamians earned leadership positions and spots in every committee of the AFL, and the union’s first five vice presidents were Black. This inclusive labor movement continued until the 1930s, when U.S. Steel—rife with Ku Klux Klan members—began to restrict job promotions for unionized Black workers, limiting access to senior positions they previously occupied.