Costs of deployment and profit margins have nothing to do with it. The US public has subsidized the cost of broadband internet deployment since the very birth of the internet, and continues to do so like clockwork every few years. Private ISPs continue to caress the books to make it seem like they're barely operating at a profit and still need more, without ever having delivered on the last promise. Taxpayers have paid for fiber to every home a few times over at this point.

http://irregulators.org/bookofbrokenpromises/