In many cases though.. the farmers have rights to the land. The farmer is leasing the rights to the land (not just the right to farm)... to do as he/she sees fit. This means hunting rights as well.

My in-laws farm over 3000 acres in Ohio. Some leased, some owned but the hunters have to come to them for permission to hunt. I'm not saying this is always the case, may be different in different areas but it is often the decision of those who pay to use the land and not that of the actual landowner.