Why, or under what circumstances, might it be hard to establish a large area of protected land?

For the answer to the question above asking why, or under what circumstances, might it be hard to establish a large area of protected land?
It is hard because of economic, political, and social reasons.
It cost much to monitor a large piece of land and to maintain it. The species in that large piece of land are different. So there can be scarcity their food. Protecting it from political leaders who want to exploit this protected land because of their greediness could cost you a fortune.