The sharp declines in mobility for lower-income groups look like the disincentivizing effects of a growing redistributive welfare state.
Look like -- but another factor suggests itself. The factory used to be the most reliable means out of poverty or for not going into poverty. Consider that Booker T. Washington recognized manufacturing was the best hope for African-Americans escaping the peonage-like conditions of the agrarian South was not in Academia (which in practice was discriminating against even white Catholics at the time) or the skilled trades. If black people had jobs that white people wanted, such as barbering, then white people found ways in which to get such jobs. Skilled trades generally got passed down from father to son. Owning and operating a business? Freedmen tried that with commerce and banking, only for the old agrarian elites to oust blacks from such activity with the aid of the first Klan. (The Tulsa riot of 1921, which happened after Booker T. Washington died, suggested that nearly sixty years after the Civil War, white people were still hostile to economic success among African-Americans to the extent of rioting. Semi-skilled work? It was made for people of physical toughness and a good work ethic. Starting in the 1960's, factory work started to move away from America altogether. It began with toys and clothing and moved eventually to vehicles and electronics.
The growth of welfare dependency was a symptom, and not a cause.
