There are a number of factors that basically require a local monopoly for terrestrial telecom. This is a feature of the market — not anything the government has done.
#1 is the universal coverage requirement — anyone receiving a local monopoly from a municipality has to agree to make service available in the entire city. Many poor or low-density neighborhoods are not profitable for even a single company to serve, much less multiple companies. Overbuilders have no such requirement to even provide the potential of service in low-income areas, so none do. A side effect of this is that overbuilders can’t approach the level of efficiency that the monopolists can (see #4) and none can be much more than a nuisance to the incumbents as long as they remain overbuilders.
#2 is that in the wealthier / denser areas of a city that can support more than one provider, there are typically 2-5 providers offering speeds of 100+ mbit. The local monopolists therefore rely on the profits from the wealthy areas to cover the losses from the poor areas.
#3 is that it’s really hard to get investment to overbuild unless it’s a wealthy area. Telecom rollouts are expensive and require taking on significant debt. For every additional overbuilder serving an area, your ratio of [households served] / [households subscribed] and the amount of overhead you have to recoup for each customer goes up. Investors will not loan you money if they think you won’t make it back.
#4 is that telecom services are a scale business where you need vertical integration to be viable. TimeWarner Cable had their backbone network with TimeWarner Telecom. That was fine until both companies split and the infrastructure was owned by two different companies. TimeWarner Cable then had to build their own backbone — which lowered their credit rating, which made every subsequent debt offering more expensive. They were trapped in a cycle where they needed to invest badly, their network was slow so they couldn’t raise prices much, but borrowing was so expensive for them it turned into a death spiral. And that’s how the #4 cable provider in the country was able to buy the #2 provider — Charter was simply more vertically integrated through Liberty Media and had a better balance sheet.
The “take rate” (how many households of the total subscribe to broadband internet — directly correlated with household income) of a neighborhood largely determines how many companies serve the area. The overall take rate of the wealthiest cities is sufficient to support at most 3 broadband providers serving a given household; in the poorest cities the government has to subsidize access for even a single company to serve the area.
Capitalism and abuse of position go hand-in-hand. I would argue that abuse of position is the fundamental driving force behind capitalism.
(These rules largely do not apply to wireless.)