A lot do that for your own protection. I plan on going out to live by myself for 2 weeks in the woods. I thought about parks here in Missouri, but they all pretty much say the same thing. I called up my Park Ranger buddy and he said i could get a major fine and even be arrested for not following these rules. The best thing to do, and what i eventually did, is to find someone with a huge bit of private property and ask them. Make sure you tell them you will be respectful and clean up after yourself. I offered to clean the guy's crop combine in exchange for letting me stay there. I just knocked on his door and he was skeptical at first but i offered to do the work and he eventually was more than happy to let me. He drove me out to a good spot with a little clearing in the trees right next to a creek with running water.
Just make sure to ask and don't go anywhere that you see purple on the trees (that means no trespassing.) You can be shot on site for that.
