In the muni where I serve on our telecoms commission, we built (before I got there) a fiber network with the anticipation of potentially offering it to tenant ISPs. We wanted the network anyways for internal municipal needs. But the economics of building an ISP on top of that fiber in a place already served by AT&T and Comcast are not great: you target a certain amount of uptake to break even, and you're not going to get it.