A recent study done by Responsive Management titled, Issues Related to Hunting Access in the United States, indicated that difficulty gaining access to lands for hunting has become a constraint to recruiting and retaining sportsmen. Adequate access to land is one of the fundamental issues that affect the future of hunting.
The survey asked hunters about possible reasons that landowners may close their land to public hunting. The top three related to the misuse of the land: irresponsible shooting, alcohol use, or other bad behavior by hunters. Other top reasons cited were property damage caused by hunters; litter;landowner wanting to allow only personal/family use of the land; and liability concerns.
Unfortunately asking landowners that have closed their land was not within the scope of this study. My reading over the years points to landowners wanting to be in control of what goes on on their land and the only way currently open to them is posting.