For example, here in California cable TV is not a state-granted monopoly. And yet, you will find close to zero overlapping cable TV regions. Why?
Because, until fairly recently, it was, in most parts of the state, a local government granted monopoly, and while the local carriers have changed hands (largely to consolidate regions and create bigger regional monopolies), there are significant barriers to entry in any local market, which means that the monopoly carriers are pretty well entrenched, with the main competition coming from alternatives to cable (satellite, services delivered over internet, though the cable providers themselves are also some of the biggest broadband providers) rather than alternative cable providers per se.
"I think trash is the most important manifestation of culture we have in my lifetime." - Johnny Legend