> Literally nothing is stopping anyone

Nothing but the power of the state, which has claimed sovereignty over all the land, regulates what you can and cannot do with it, and will use deadly force against you if you fail to comply.

I once added up the total calorie content of all the yearly hunting it is legal to do where I live, if a hunter were maximally successful, and it would get one person through May.

All the land one could reasonably sustain a living on has long since been claimed, those claims being backed up by (you guessed it) the power of the state. The only land left that one can just walk off into is the land nobody wanted during the settlement period, because they could not find any way to live on it.