Why does rubbing your fingers on stainless steel remove the smell of garlic?

The sulfur from the garlic is attracted to and binds with one or more of the metals in stainless steel. Formation of such compounds is what makes stainless steel stainless, after all. Onions and garlic contain amino acid sulfoxides, which form sulfenic acids, which then form a volatile gas (propanethiol S-oxide), which forms sulfuric acid upon exposure to water. These compounds are responsible for burning your eyes while cutting onions and also for their characteristic scent. If the sulfur compounds bind to the steel, then the odor is removed from your fingers.