The answer to 'why is my roof vent worn out' is that roof vents can become worn out over time due to exposure to the elements and general wear and tear. Common causes include damage from weather, UV radiation, and physical impact. Symptoms of a worn-out roof vent may include cracking, warping, or deterioration of the materials.
In many cases, a worn-out roof vent can be repaired or replaced relatively easily. However, if the damage is extensive or the vent is an integral part of the roofing system, it's best to call in a professional roofing contractor to assess the issue and provide the appropriate solution.