They were very sought after, but it was very common for folks to put their money in a sealed ceramic pot to protect and hide it, either buried under the floor of their home somewhere or outside in some secret spot. There were regular wars, plagues, invasions, and other civic chaos that left many of these hidden troves long buried until someone later found them. Ancient peoples buried a lot of metal artifacts for burials or rituals (the Celts buried a lot of weapons in their rites) that have been recovered as well. Lots of circumstances need to line up, but the ancient past had many very chaotic eras. With metal detectors large numbers of troves are being rediscovered.