Why is chewelry needed? 

Chewing can be a very effective way to calm and self-regulate, especially if you're anxious or stressed or need to focus.  It’s similar to how some people bite their fingernails when they’re nervous, or pace back and forth, or tap their foot, etc.  Needing to chew on non-food items is often sensory-related, but not always.  For a lot more background on why some people need to chew,  check out this article.