Farmers don't wear high fashion, or even fashionable clothes because of the dirt and smell that farms have!
Also for comfort reasons as well.
The clothes they wear you relate to a farm yard & there isn't any disagreement with what they are wearing, so there is no contrast against the location.
The look we want is a contrast look against the farm yard location, so we couldn't dress our model in 'farmers clothes' as there would be no contrast.