The answer to 'why is my grout filthy' is that grout is prone to staining and discoloration over time, especially in high-traffic areas. Common causes include spills, dirt buildup, mold, and improper cleaning. Symptoms may include dingy, discolored grout lines that detract from the overall appearance of your floors or walls.
To address this issue, you have a few options. For mild cases, you may be able to clean the grout yourself using a specialized grout cleaner and a stiff-bristle brush. However, for more stubborn stains or deeply embedded dirt, it's often best to call in a professional cleaning service. They have access to powerful cleaning solutions and equipment that can effectively restore the grout to its original condition.