This question here goes into the whole buried treasure thing. Thread here.

Though I don't think they ever mention that stories of buried treasure (be it buried by pirates, early Spaniards, or what have you) and people trying to find it have been around almost since the time of the settlement of the colonies themselves. The early leaders didn't like the stories so there wasn't much openess of pursuing this stuff, but the late eighteenth and roughly first half of the nineteenth century had tons of people looking for secret treasures. There is some relation to "God Rewarding Them" and "Finally, Reward for Working the Earth For So Long" in there. These traditional American buried treasure stories that spanned the entire coast of North America in the 19th century that frequently tried to claim that pirates buried treasure on their coast (it seems people have always been obsessed with the idea of finding riches) probably inspired Treasure Island in some part. So the cliche is almost as old as the pirates themselves. For more on America's affair with hunting for buried treasure, see this article: Taylor, Alan. “The Early Republic’s Supernatural Economy: Treasure Seeking in the American Northeast, 1780-1830.” American Quarterly 38, no. 1 (1986): 6–34.