Not quite political, mostly simple economics…
Phone, television, and internet require a massive upfront investment, hundreds of thousand to millions to enter a new market. The must purchase right of way to build utility poles or underground conduits (or rent space in existing facilities). They must physically string wires or fiber optic cable on these poles. They must build local head house facilities to power and provide signals to these wires.
Only once this massive investment is made can they then start marketing and connecting customers!
Cable companies back in the 80’s built their networks from scratch. They entered into exclusive contracts with TV channels that precluded competition from phone companies to help recoup their investment. Today, these contracts are expiring, or regulations are forcing them to allow the phone companies to provide competing television service.
Politics probably enters into which company gets which market, but a lot of it that it is simply too expensive to duplicate service once one cable company enters. The phone companies have an advantage entering the TV market, because they have an existing network connecting to nearly every house in a market. With a few new servers and spot upgrades, they can offer DSL internet and limited TV service over the existing wires. Only in extremely dense and well populated areas might you see competition among peers offering perfectly duplicate services.