Supply and demand?

Monopolies are bad. Everyone knows that, yet it seems like our societies are remarkably bad at preventing their existence. I am certain that this is quite deliberate and not a coincidence - that powerful interests benefit from the monopolies´existence and thus allow them to operate and thrive.

One such example are cable and internet providers. Where I live in Brooklyn, the only cable provider we have access to is Cablevision, while in other parts of Brooklyn, people can only deal with Time Warner Cable. There are no alternatives where I live. The companies seem to have carved the borough between themselves, not unlike colonial overlords and the users are stuck with companies where all normal rules of supply and demand, quality of service and consumer choice simply do not apply.

What I don´t understand is why on earth these companies are allowed to operate in this way. They should be required to compete with each other. The result of this system is a cable operator like Cablevision which has left us with no service (no tv, phone or internet) for a week now, and they know that they can get away with doing nothing and providing incredibly poor service it since we cannot take our business elsewhere. This seems to be pretty common. We´re either stuck with them or we can simply go back to dialup, which, by the way is starting to look pretty tempting.