Before Hershel took over, Dale was essentially the moral compass of the group. His age, his experience and his almost white beard made him a sort of elder than the other survivors looked up to. He was a very outspoken member of the group who often argued to do the right thing, even if it was the most challenging option. For Dale, his facial hair suits his personality as well as his back story. His lost his wife Irma to cancer and found it difficult to deal with her death as they had planned on travelling in the RV. She died before this could happen. He then became depressed and decided to do the trip alone, so someone in this mindset isn't going to be the perfectly clean shaven man who is always taking care of his appearance.
