The answer to 'why is my dryer vent grimy' is that a buildup of lint and debris in the dryer vent is a common cause of a grimy vent. Over time, lint and other fibers from clothes can accumulate in the vent, restricting airflow and creating a grimy, clogged appearance.
This lint buildup is often caused by not cleaning the vent regularly, which allows it to gradually become blocked. Symptoms of a grimy vent include reduced airflow from the dryer, longer drying times, and even a fire hazard if the lint is allowed to accumulate. The solution is to clean the vent regularly, either by doing it yourself or calling in a professional dryer vent cleaning service.