Why are pirates always shown drinking rum?

It is a Caribbean spirit. And most English pirates operated in the area because that is where the Spanish and or French were. The local drink. It was cheap.
Plus, privateers would bring Rum back to Europe to prove they had been there.

Because rum is yum. Seriously though, from what I can find out, it does have to do with hydration. From the 1700s sailors were given a rum ration. According to Forbes, the reason for this was because stored water and beer would only last so long on board a ship and rum lasted much longer. It also kept the sailors happy during a time when conditions onboard a ship were not so nice. I’m sure pirates drank it for the same reason. They’d also have been able to steal it from the increasing number of ships sailing to the Caribbean and far flung places.

The Wikipedia page credits the rum rations were implementation in the British Royal Navy to Admiral Edward Vernon who was apparently known as ‘Old Grog’ in 1740. Within 20 years the navy started to add lime or lemon to the rum to help prevent sailors developing scurvy. The rum ration wasn’t stopped until 1970 in the UK. I guess they were pretty well assured the sailors would get their daily vitamin C requirement by adding it to the rum.

Because they’re all out of Dr. Pepper.

It helps ‘em rum-ance wenches.

What @josie and @Earthbound_Misfit said. Also, people throughout history have shown great ingenuity in making alcoholic drinks out of local ingredients. Some of my buddies made prison wine in a bathtub when we were underaged in college. It was nasty. People are creative and will go to great lengths to get hammered, but in the past the drinking water also wasn’t that great. They turned to milder alcoholic drinks like beer as a safer alternative. Also, controlled fermentation was one way to preserve perishable foods before refrigeration existed, along with salting/ drying and pickling. A lot of our best foods came out of that, like sauerkraut, salami, pickles, and jam.

Anything with sugar or starch in it is fermentable, and can be made into alcohol. Rum is made from molasses (or sometimes, fresh sugarcane juice), and sugar canes grow in hot, tropical areas. In a hot climate and over long sea voyages, a product that is non-perishable is very helpful. Oak barrels were the most widely available large containers back then. Aging a spirit in oak gives it a rich, vanilla/ toasty flavor. Since rums were so often transported and stored in oak, it became a traditional part of the “recipe” for making rum, and is still used to this day.

And pirates, with their devil-may-care swashbuckling ways, love a good drink. :)

Because they feel guilty about raping and pilaging and want to drown there sorrows.

Why is the rum gone?

Rum was used to make water bearable to drink. Plain water was untreated and usually unsafe. Mixing it with rum (to make grog) helped. A bit.