Cabin air filters dirty up pretty fast!
Obviously, there is going to be some variation in how dirty your cabin air filter gets based on the design of the system and where you drive and park the vehicle but they don't last long.
After 1 year and 17K miles of driving, the cabin air filter in my Ram 1500 was completely brown and covered in a layer of leaves. I make it a point to at least check and usually replace my cabin air filter every year in the fall. If you are reading this, you should do the same!