Since it’s very dry and has long shelf life it can be stored for long periods of time without refrigeration. That, with the fact that they are easy to make is one of the main reasons sailors and soldiers used to eat them. To soften them, they would dip them in tea of coffee. They are also light to carry and can replace bread.
The name derives from the British sailor slang for food, "tack". It is known by other names such as brewis, cabin bread, pilot bread, sea biscuit, sea bread, ship's biscuit, or ship biscuit.
It's not clear when people first began to make hardtack, but it’s quite probable that it was in prehistory. Prehistoric people boiled grains; they cooked grains and added vegetables and herbs to the mixture; and sometimes they ground it into a powder, mixed it with water, and dried it on a hot stone. Six thousand year-old unleavened biscuits have been found in Switzerland.
Hardtack was a part of the staple diet of English and American sailors for many centuries. Christopher Columbus took unleavened bread with him on his journeys. Sailors referred to it as sea biscuit, sea bread, ship biscuit, Midshipman’s nuts, and pilot bread. During the early settlement of North America, the exploration of the continent, the American Revolution, and on through the American Civil War, armies were kept alive with hardtack.
The soldiers called the biscuits “sheet iron crackers”, “teeth dullers”, or “worm castles” in references to the weevils and maggots all too often found in the hardtack boxes. It appears that it was first called hardtack by the Union Army of the Potomac; although the name spread to other units, it was generally referred to as hard bread by the armies of the West.
Source: What's Cooking America
The rich history of this biscuit shapes peoples views on it today. It was never a delicacy, however the fact it left a bad taste in peoples mouths is reasonable, seeing how it's closely linked to war. The fact of the matter is, hardtacks need rebranding. They could be made with new ingredients and since we wouldn't store them for years, there would be no need to break them with rocks. Other simple biscuits are still being made and consumed all over the world, so there's no reason why hardtacks shouldn't.
Discover more: Biscuit Types