In the country called Krohn there is a territory known as the Dragon-Lands. The Dragon-Lands are both a vast, largely unexplored, self-contained area ringed with cliffs as well as any high place, any mountain. Krohnian dragons are winged cliff-dwellers, possessed of the surefootedness of goats or--to give a better visual image--salamanders. And one of the chief salient features of the dragons we know, that they hoard treasure, has an interesting counterpart in Krohnian dragon society. There are vast stores of wealth in the caves of the Dragon-Lands, not just the stereotypical mounds of gold crowns and rubies and pearls, but anything that anyone might consider treasure--piles of nuts amassed by squirrels, say. (It is human-centric to consider valuable only such baubles as gold crowns and rubies and pearls.) The land itself is rich--plant wheat and see your crop yield a hundred-fold, sift your fingers in the gravel of the streams and find diamonds.
All of this belongs only to the dragons, though they will be the first to admit they weren't the ones who went out and gathered the treasures blanketing their cave floors. Some may tell you the dragons have conquered the territory and fight to keep it for its wealth, but this seems to me a simplistic answer. What are gold and jewels anyway, to dragons? Or squirrel-gathered nuts, for that matter? Ask a dragon why they have such a massive stockpile, and they will say that their task is to guard it.
Indeed, they are the only ones who can keep it. Plant that wheat in the Dragon-Lands, prospect for gold, hunt for gems--if you aren't a dragon, it will enrich no one but yourself. For though the land is rich, any non-dragon living in it will become barren. So it remains unexplored.