As far as I know in many markets they can't, the monopolies were granted by cities. Comcast even sued some cities trying to build infrastructure: http://www.theverge.com/2015/5/1/8530403/chattanooga-comcast...

In a sense, yes. I would argue that the cabled infrastructure is not a natural monopoly at this stage of technology development, but the pre-existing regulatory framework and the local municipalities treated it as such. The effect was a market where local monopolies were bought and sold. Which leads to no free market for buying and selling last mile Internet access.

To build a parallel tax-funded infrastructure like the fine article says, would be just silly in those monopoly markets (instead of enabling commercial competition first; not sure if New York in particular has any meaningful competition, so this may not apply there).