Several things happened.
1. In some parts of the country there was an infuson of Eurasian boar blood from boars imported for sport hunting. IMO: This a biggie, many of the feral hogs in this area have Eurasian boar blood. Those hogs often refuse to bay when chased by dogs. They simply keep going until the dog tires out. One evening last week i saw a sounder of about 40 wild hogs about 100 yards away. Shot at one with my muzzleloader. Those hogs did not scatter at the shot, they bunched up tight and took off.
2. Here in OK folks are releasing hogs into the wild. They often trap wild hogs in one area and transfer them to another area that has few hogs.
http://newsok.com/panhandle-man-acc...ased-feral-hogs-into-the-wild/article/5377286
3. Most deer hunters refuse to shoot hogs.
4. In some states, like OK, it is illegal to hunt wild hogs at night with a gun. Here in OK we are not allowed to use a centerfire rifle to hunt hogs in the WMAs outside of deer season.
5. The proliferation of so called hog "hunting ranches": Escapees from these facilities are common. In order for a fence to be "hog proof" the chain link must be buried at least two feet into the ground. IME: None of the "ranches" have adequate fences and no one ever checks them.
6. During a good year when when acorns and pecans are plentiful the hog population really takes off. The sows have bigger litters.
7. i'm a hog trapper and hunter. We give away an average of 150 field dressed wild hogs each year. You get one chance to catch wild hogs. A hog that has been trapped and released or escapes will very seldom enter a trap.