It's really tough (i.e. not just strong but ductile as well i.e. able to stretch more without fracturing like a brittle material would) and relatively cheap to

It's really tough (i.e. not just strong but ductile as well i.e. able to stretch more without fracturing like a brittle material would) and relatively cheap to manufacture (both because the industrial process is scalable, and because iron is incredibly abundant). When cost isn't an issue, you don't use normal low alloy steel - you use expensive alloying elements like chromium for corrosion-resistant stainless steel or more relevant to this comparison, nickel for maraging steel which is several times as strong as ordinary steel.