I think one important aspect of this is that the infrastructure can’t be put up without government permission, as it is on public property. I would bet that government had a large role to play.
Besides, a company has to recoup the startup cost before truly profiting. If it takes a long time to recoup those costs, so that no one else will put up the money for a similar infrastructure, is the company engaging in evil monopolistic policies? If the company makes back its initial investment quickly, then others will be willing to make a similar investment. Even in the first case, over time the cost for another company to put in place a similar infrastructure will generally be falling. And there’s always a possibility that new technology can provide a similar service with a different (cheaper) infrastructure. Using the government to prevent a new company to enter a market is the best way to keep a monopoly no matter what.