The answer to 'why is my window dirty' is that there are several common causes, including environmental factors, improper cleaning techniques, and buildup of debris over time. Windows can become dirty due to things like dust, pollen, rain streaks, hard water stains, and even bird droppings.
If your windows are looking dull or have visible dirt and grime, it's likely time to give them a thorough cleaning. You can often handle this as a DIY project, but for hard-to-reach or heavily soiled windows, it may be best to call in a professional window cleaning service.