Although thermodynamically feasible,in practice,magnesium metal is not used for the reduction of alumina in the metallurgy of aluminium. Why?

(N/A) According to the Ellingham diagram,magnesium can reduce alumina $(Al_2O_3)$ at temperatures below the point of intersection of the $Al_2O_3$ and $MgO$ curves. However,this process is not used in practice because it is economically unviable and technically difficult to maintain the required temperature conditions.