Often because I'm anxious and the actual act of chewing calms me (as in I can chew gum and it has the same effect). Some of the time because I feel this deep cavernous emptiness inside that I'm desperate to fill. And then the rest of the time because I'm bored. I'm anxious for who the heck knows what reason, my mind is constantly catastrophizing and worrying about nonsense and can't stop ever, the emptiness comes from an unfulfilled life, and the boredom's from having no structured activities in my life right now (no school, work, etc.). I'm working on changing some of these things, but it takes time.