First, 'Stainless' is not a single item and in fact a wide variety of alloys with sliiiightly differing compositions which confer more or less corrosion resistance in favor of other mechanical attributes of the finished product. I have read (but must admit I do not know the accuracy of the claim) that Tesla went with a harder yet less corrosion resistant form of stainless for the cybertruck.

Second, while they see regular use the profiles of wear for e.g. cookware are very different than that of a car's body. For one, you likely thoroughly clean your cookware relatively soon after using it. How often is the car thoroughly washed down? The outside chemicals, road de-icer, quantity of UV or other environmental effects that differ between the daily life of your average chef's knife and a given cybertruck also very much play into it.