A paper by James Valvo published by Americans For Prosperity notes,

Easily the biggest problem with municipal projects is that they commit taxpayer money to projects that nearly always run over budget for construction, are not financially sustainable once they are built and rely on future subsidies to provide so-called “free service.” As is always the case when governments enter the free market, distortions in price, customer service and availability hinder competition and ruin what could otherwise be a profitable
venture.

See: Municipal Broadband’s Record of Failure: A Profile in Market Intrusion.