You don’t see that at managed campgrounds because you will be fined.
Thus proving the superiority of private property over the complete anarchy of the commons.
The small group ruining things is akin to the broken window. It requires some kind of regular process / hygiene to maintain the system in a good enough condition.
As I understand it, an anarchist camping group (for lack of a better name) could still collectively agree on and enforce rules - in many ways still a "managed" campground, just with more shared ownership
In a sort of ceremony where you swear to follow the rules of the - oh I don't know, country? - that you're joining?
I try to do this at work when a new engineer tries to argue that the current system is overcomplicated and there is an easier alternative. Just ask questions, point out edge cases and watch them gradually rebuild the current solution.
Doesn't always work, sometimes the current solution actually sucks. But more often than not they come to understand that by the time they're finished ironing it the details, their proposal is not meaningfully different from what we have.
Even if they do have a monopoly, a large group with an effective monopoly on paying campers over some timeframe can negotiate an agreement for reduced or no fines.
Anarchy is about power relations. If they're relatively equal, it's anarchy.