Private firms with monopoly power never last, unless that monopoly power is augmented by the government.
The Comcast "monopoly" is in the process of falling apart, on one side from Netflix, Amazon, and Hulu and on the other side from Google fiber, 5G wireless, mesh networking, and perhaps even the Elon musk LEO satellite Internet plan.
The Willis Graham Act nullified the Kingsbury Commitment by which the government had tried to stop the unfettered expansion of Ma Bell, since it hadn't actually worked the government shifted to trying to regulate Ma Bell itself through the ICC (and the FCC a few years later).
The Comcast "monopoly" is in the process of falling apart, on one side from Netflix, Amazon, and Hulu and on the other side from Google fiber, 5G wireless, mesh networking, and perhaps even the Elon musk LEO satellite Internet plan.