Local government must approve each company that uses the telephone pole right-of-ways. But the cities and counties generally already have a contract with Comcast, ATT and whoever and this contract may prevent competition regardless of the government's desires. Moreover, these monopolies can mobilize their state and national level allies (some state was trying to outlaw municipal broadband utilities recently, for example).

The thing about State-sanctioned monopolies is that since their whole revenue stream depends on their relation to governments, they spend a substantial portion of their income getting influence within our presently rather corrupt government system.

It's hard to companies that operate more on the "open market" to move into a "turf" of this sort.

That depends on the state.

Often that licensing is done at a statewide level, rather than city by city.

The franchise agreement is to actually offer service - not to place crap on the poles.

There is a bit of misinformation in your post. The practice of granting exclusive cable franchises has been illegal since 1992. Many places still have one franchise simply because its not desirable to compete against the incumbent cable company.

My city actually signed Comcast into a legal monopoly to get them to bring service here in the 80s and 90s. That deal is still good, and states that they will be the sole provider of cable TV service at least until the end of this decade. From what I've seen, this was a common practice, and has apparently happened in a lot of smaller towns.

It happened a lot in smaller towns because without the carrot of the monopoly grant, it would've been undesirable for companies to wire up those little towns at all.