Because the bronze age was not a wet copper smelting! The hydrometallurgy of copper didn't happen until the appearance of iron ~ The following is the information:

Around 2000 BC, China entered the Bronze Age, and during the Warring States Period around 500 BC, China entered the Iron Age. Copper is the earliest metal used in human production. Copper is very abundant in nature and easy to process. At first, people only used the natural element copper existing in nature, and the development of production prompted people to find a method to obtain copper from copper ore, that is, pyrometallurgical copper. Man discovered and used iron later than gold and copper. First of all, because the natural element iron on the earth is very scarce, the metal activity of iron is stronger than that of copper and it is difficult to reduce from iron ore. Its melting point is much higher than that of copper and it is more difficult to smelt than copper. Judging from the earliest time when humans used various metals, the less active metals were used by humans earlier. About 200 BC, our people realized that copper in copper salt solution could be replaced by iron, and it was the first country in the world to smelt copper by wet process.