I think the fact that they’re pretty, nonreactive, rare, and were available very early is huge here. Gold is just there sometimes, little flakes and beads washed to rhe surface. It’s one of the only metals you find non metallurgical cultures using. From there it became valuable for jewelry and ritual objects because of its rarity and appearance, and once you have something durable, reworkable, and more desired than possessed it becomes a really easy thing to trade, especially when cross culturally valued.