The answer to 'why is my carpet dirty' is that there are several common causes, including high foot traffic, spills and stains, pet accidents, and general wear and tear over time. Symptoms may include visible dirt, discoloration, and matted or compacted fibers.
Some solutions to consider are regular vacuuming, spot cleaning for spills, and professional deep cleaning every 12-18 months. While simple maintenance can be done yourself, it's best to call in a professional carpet cleaning service if the carpet is significantly soiled or damaged.