There's plenty of work around the farm to be done over winter (basically, all kinds of work that isn't strictly necessary around harvest season will be pushed out to whatever other time there is in the year). You still have farm animals to handle. There are repairs to be made. Trenches to dig. And as the winter comes full force, given how low-density an energy source firewood is, you at least needed to regularly get out to haul and process fuel for heating.

Etc. My life experience is only slightly farm-adjacent. I'm sure someone who grew up on a farm can contribute more examples of winter work.