Why is copper extracted from low-grade ores by hydrometallurgy?

(N/A) Copper is extracted from low-grade ores using hydrometallurgy. The ore is leached using acid or bacteria. The resulting solution contains $Cu^{2+}$ ions,which are then treated with scrap iron or $H_2$ gas. The reaction is: $Cu^{2+}_{(aq)} + H_{2(g)} \rightarrow Cu_{(s)} + 2H^+_{(aq)}$.