Changed the title of the thread from “Why do they call it stainless steel of it stains anyway?” to “Why do they call it stainless steel it stains anyway?”.
In the beginning, stainless steel was sold in the US under different brand names like "Allegheny metal" and "Nirosta steel". Even within the metallurgy industry, the name remained unsettled; in 1921, one trade journal called it "unstainable steel".
Stainless Steel is extremely durable and corrosion resistant. Nothing is invincible, but proper care will make it nearly indestructible and stain free.