Why your dog is not barking will depend upon its cause. For example:
He is Hoarse as a Result of Over-barking
Your dog may have been barking for a while and have overused his vocal cords. A lot of barking can lead to inflammation of your dog’s vocal cords and cause him to have laryngitis. After giving his voice a rest, his bark will be back. This occurs commonly during a kennel stay.
Breed
Certain breeds of dogs tend not to bark much, if at all. For example, Basenjis and Beagles make a sound that is more like a humming noise than a bark.
Personality
Each dog has his or her own personality. Some dogs may not like the sound they make when barking or he may prefer to whine or make whimpering sounds. Your dog may be laid-back and easy-going and feel no need to bark.
Health Condition
There are conditions that can lead to your dog not barking. These include laryngeal paralysis, infections and a tumor. In laryngeal paralysis, the structure of your dog’s larynx or voice box will be altered and/or the function will be impaired. In laryngeal paralysis, the laryngeal muscles become weak or paralyzed and the cartilage that is usually supported by those muscles collapses in. In the case of a tumor, one can grow in the larynx or trachea of your dog. One such tumor is called Chondrosarcoma, which is a slow growing malignant cancer. This tumor can get in the way of your dog’s ability to eat and breathe and can impact his voice.