The answer to 'why is my steam cleaner stained' is that steam cleaners can sometimes leave behind mineral deposits or discoloration, especially if you have hard water. This can happen if the water in the steam cleaner isn't properly filtered or if the machine isn't cleaned and maintained regularly.
Some common causes of staining include mineral buildup from hard water, leftover detergent or cleaning solution, or even mold or mildew growth inside the machine. This can lead to unsightly stains or streaks on the surfaces you're trying to clean.