Bronze has a lower melting point compared to Iron making it much easier to work with. I think you also have to invent charcoal first to reach the temperatures necessary to melt iron ore.
Iron was originally produced without melting it at all. Instead, iron ore was reacted with reduced gases, and a flux (limestone) causes the silicate contaminants to melt instead. The solid iron that's obtained (sponge iron) is then forged into shape (and also beaten to remove residual silicates.)