#1 Most dogs have a natural desire to chew. It’s fun, it passes the time, and it’s a self-rewarding, self-reinforcing activity (for example, if she’s chewing on something that tastes good.)
#2 Chewing provides a nervous, bored, or lonely dog with an outlet for her emotions. To an anxious dog, the repetitive act of chewing is soothing – it’s the doggie equivalent of comfort food.
#3 Under exercised dogs often use chewing as a way of burning up nervous energy and giving themselves something to do.