There is no technical reason why the US could not be rewired for fiber and high speed internet be made available for everyone.
Of course, the cable companies don't want to hear this as it would destroy their industry. The satellite TV companies would be hurt as well. And most importantly, it would mean that the telephone carriers would actually have to spend money, a lot of money for the job to be done right. Instead, they will continue to do things on the cheap to maximize short-term revenue over the long-term rewards.
Why do you think so many pushed BPL for so long? They wouldn't have to rewire, especially in the rural and lighter population areas, just use the electric grid! Much, much cheaper that way!
Follow the money.