If the municipality owns the poles and the power company this is comparatively easier. In places that own both, like Traverse City in Michigan, Chattanooga TN, or Longmont CO, this model can be incredibly effective. The problem, at least in my part of the world (Michigan) is that most municipalities do not own the poles or the power company. The power company is instead a large publicly traded corporation, albeit with strong regulation.

Adding regulation to force power companies to run dark fiber on new runs only addresses part of the problem. You still have to deal with the millions of miles/kms of installed grid that sees proactive maintenance _maybe_ once a decade.

Not to mention the state laws in dozens of states that place onerous rules on municipalities installing their own broadband service, or even outright forbid the practice entirely. These laws are often the result of ILECs lobbying state governments or using their lobbying groups to directly write "model legislation" that state governments subsequently adopt.