The answer to 'why is my hardwood floor filthy' is that there are several common causes, including heavy foot traffic, lack of regular cleaning, pets, and tracked-in dirt and debris. Symptoms can include a dull, grimy appearance, discoloration, and even visible scratches or damage.
Some key solutions are to sweep and vacuum the floors regularly, use a hardwood-safe cleaning product, and consider having the floors professionally cleaned and refinished if the dirt and damage is extensive. It's generally best to call in a professional cleaning service if the floors are very dirty or damaged, as they have the right equipment and expertise to restore the floors safely.