@Deglassco Those machines were actually invented in the 1920s. Until WW2 the field workers had little if any cash income and no way out of that life.
The economics hadn't really changed much since the Civil War. You were now free to quit, but only to walk somewhere else and take a similar job under the same conditions.
WW2 offered them new options - military service and manufacturing jobs. Once they had cash and a real job, nobody really wanted to go back to picking cotton.