Rednecks and Lawyers
Unfortunately Rednecks and Lawyers have ruined it for everyone. The good old days of knocking on someones door and getting permission to hunt for free are fading because of this. Rednecks will shoot up and trash a field of crops just almost as fast as a herd of hogs. There are a select few idiots that call themselves "hunters" that ruin the fun for everyone (by not hunting ethical/safe, littering, etc). Then if someone gets hurt on your land, you get sued. If you were a landowner, would you give out-of-town strangers free hunting rights to your land?
Feral hogs here in the southeast are nothing more than a plague for some people, and are not valued anymore than coyotes. There are several farmers that will grant free hunting rights, but it is all about "who you know." If you know someone that knows a landowner and can give you a reference as a respectable "sportsman" it will make it much easier.