Seems to me that stainless harware items--fasteners mainly--are worse and worse this way as more and more (if not almost all) of it comes from the third world and the orient. Plenty of recycled razor blade and who knows what else in there. Also, if the factory equipment that rolls the threads is not dedicated to only doing stainless, or very thoroughly cleaned between material runs (Hah!) there is a fair amount of ferrous particulate smooshed into the stainless parts.
Dave