Treasure Island is largely responsible for why we think pirates buried treasure, but they didn’t.
Robert Louis Stevenson’s 1883 tale of pirate adventure, Treasure Island, has done more to shape our idea of colonial era pirates than anything else. How we think pirates dressed, how they behaved, to how they spoke (although some of that was English actor Robert Newton’s exaggerated West Country accent in the 1950 film adaptation – which is the basis of most “pirate speak”), Treasure Island basically defined the pirate genre. It also popularized the fictional idea of treasure maps and buried treasure.
You can’t bury perishables
Pirates didn’t bury treasure for a host of reasons. For one, if they were lucky enough to raid a ship loaded with money or jewels they turned around and spent it – it didn’t stick around long enough to be buried. A bigger reason however was that gold, silver, & jewels were a small fraction of what pirates typically got to steal. Most looted booty were normal trade goods (sugar, alcohol, dyes, tobacco, cloth, timber, food, etc). The seas were the highway system for moving all manner of commercial merchandise and most of pirates stole would rot if left to sit around for extended periods of time (burying them being even worse). It was more typical that pirates would sell these goods in port towns and, again, immediately squander the money they earned. Most pirates never accumulated enough wealth to even have the option of burying it somewhere.
Ultimately it’s a myth that pirates buried treasure … but with one famous exception. In June of 1699 Captain William Kidd, while sailing to New York where he knew he was a wanted man, took the preventative measure of burying some pirated treasure on Gardiners Island off the East end of Long Island. He hoped to use this treasure as leverage in his future trial, which failed as he was eventually convicted of piracy and executed.
Added info: You can find a copy of Treasure Island in lots of places but it’s also available for free as an audio book on archive.org.