EPB does have a very nice "smart grid" that uses fiber optic lines to connect to stations positioned all over their network that monitor the condition of the connected grid and can rapidly shut off power to a very localized area. They realized that they still had quite a large bit of bandwidth remaining, and decided to start an ISP.[1]

1- This is all based on what I recall from conversations with EPB higher-ups when I spent a day chatting with them for a school event.