During the period of 1930s America and the world was going through the Great Depression, it was a period of hardship when many were unemployed and in poverty. Folk music developed during this period because people needed a music genre that could sustain faith and eloquence and push them forward.
Also, in that period Communism was starting to emerge in America and this policy was called the Popular Front. The Popular Front made Folk music more popular, this music genre would talk about labor, farm, workers by creating feel-good rhythms.