Why is casting done with cast iron instead of copper?

casting is usually done with the melting of pig iron comparing the yield strength and tensile strength with copper which is far better than copper.it is used used for casting(cast iron)
copper tensile strenth-32 ksi
grey cast iron tensile strength-50ksi
hardness
copper-42(brinell scale)
grey cast iron-260
uses-engine cylinders,gear wheels,machine tool bases,gear surfaces,high strength application,resistant to heat and corrosion
the strength is required for making these material therefore cast iron is used(alloy of iron carbon and silicon)
thanks and regards
sunil kr
askIITian faculty