Because Stainless Steel != No Rust Ever... kind of a major "duh" for anyone who's ever owned a stainless pocket knife, or even silverware. You don't even need to read the article, it should have been obvious to everyone - particularly the designers at Tesla.
There's a fairly good reason modern vehicles are mostly made from Aluminum and Plastic.
There's a fairly good reason modern vehicles are mostly made from Aluminum and Plastic.