If you worry about the cleanliness and look of your carpet, you probably vacuum it regularly. Great job on doing that and we encourage you to continue. Vacuuming is a great way to help reduce the daily accumulation of dirt, but you should consider professionally cleaning your carpet at least once a year.
Vacuuming picks up much of the surface dirt but cannot penetrate down to the deeply embedded dirt and grime. As people continue to walk and tread on the carpet, that dirt gets ground down further and deeper, making it harder to extract while damaging the fibres of the carpet.