UNESCO World Heritage sites are created when their host country submits a nomination. If the host country doesn't have the resources to submit that nomination and show that it's capable of preserving the site, it doesn't get added to the registry.

The fact that wealthier countries have more resources to put towards preservation and so nominate of their own UNESCO sites is big problem with the whole system. The Eurocentric bias of the UNESCO committee's selection of which sites actually make it onto the list is another one that's been debated for a while.