Why are metals like sodium, calcium, magnesium, aluminium etc. obtained by electrolytic reduction?

Metals like Na, Ca, Mg, Al etc, which are high up in the activity series are electropositive elements and possess a high affinity for oxygen. So their oxides are very much stable and cannot be reduced with common reducing agents like carbon. So carbon reduction process cannot be applied to prepare these metals. They can only be prepared by electrolytic reduction of their fused chlorides or oxides.