"As a non musician and wanting to offer at least some sort of plausible explanation, said - "Well most folk singers like to sing unhappy songs, so by slowing it down they can make it more of a ballad"

Don't know that I agree with this statement, Villan. Perhaps folkies just don't shy away from songs that are not uptempo. Most of the folkies I know sing a broad spectrum of material, and yes, some of it is 'unhappy'. But much of it is positive, enlivening and enlightening. IMO.