The answer to 'why is my dryer vent dusty' is that a dusty dryer vent is usually caused by a buildup of lint and debris in the vent hose or ductwork. As the dryer pulls air through the vent to expel hot, moist air from the dryer, small lint particles get caught in the vent and accumulate over time.
A dusty vent can indicate that the vent needs to be cleaned out, as lint buildup can restrict airflow and cause the dryer to work harder, leading to longer drying times and potentially even a fire hazard. Homeowners should clean the dryer vent at least once a year, or more frequently if they notice the vent getting dusty.