Might have something to do with the swine being ritually unclean animals. Who knows that an image of thousands of pigs stampeding downhill to drown in a lake might not have brought a giggle or two to the observant Judean of the day.
Certainly would plow the land for plantings ! I once read of a theory that some people keep pigs for excavation and archaeological operations ... theory indication of that which is really not known ... disclosure of Uncertainty in theory!