The known solution to this is local loop unbundling, but the ISPs lobbied their way out of that more than a decade ago.

This statement is usually made without any substantive evidence to support it, primarily because every monopoly, in practice, can only truly be a monopoly when the government mandates it. When firms are forced to compete on the open market, without the option of non-market strategies, someone will find a way to move in and compete.

This is actually self-evident in the fact that these companies are actively engaging in non-market strategies. There would be no need to practice such tactics if they could simply hold a 'natural monopoly'. Others certainly disagree, but for me, this argument is the one I find most compelling.