Stainless steel still corrodes under harsh conditions. One of the mechanisms for why stainless steel is has low reactivity is through passivation. The elements

Stainless steel still corrodes under harsh conditions. One of the mechanisms for why stainless steel is has low reactivity is through passivation. The elements mixed into stainless steel alloy quickly form a thin oxide layer in normal atmosphere which prevents further corrosion similar to aluminum or titanium. That's good enough for structural use but not the same as actually chemically inert elements. There is also aspect of what happens in more conditions like being pulverized to the nanoparticle size or vaporized and deposited at few atom thin layer. Silver and copper actually have better thermal and electric conductivity than gold, but they don't have the other good properties gold has. Also it's at the bottom of periodic table (usable part) which might be important for certain interactions and correlates with extremes of multiple properties. There is one more row lower, but most of those elements are radioactive, not occurring naturally or both, which eliminates almost any practical use, complicates research and introduces new weird properties.