I think it’s odd that they’re not. They’re generally portrayed as liking nature, and nature has no problems with animals killing and eating each other. I’m a vegetarian because I care about the individual animals, and I’m not a fan of nature and I would never become a druid unless it’s part of overthrowing the natural order.
But going to a restaurant and buying a loaf of bread is equally unnatural. It’s not like that would get them pegged as vegetarians specifically. Also, weapons and armor (metal or otherwise) are unnatural. Adventuring is unnatural. Supernatural powers are unnatural.