Hi Acrica, iron is in the middle of the reactivity series and not so reactive. Its oxide is comparatively not so stable. Therefore, iron can be readily extracted by reduction of its oxide using carbon. However, sodium is much higher in reactivity and forms a very stable compound in this case, with chlorine. It is extremely difficult to decompose such highly stable compounds to extract its elements. Therefore the highly energy intensive (and rather expensive) process of electrolysis is needed.