So TWC and Comcast are last-mile providers...
But they wield out-sized power as they are some of the few providers who can attach that last-mile to the network or a backbone.
They own the cooper or fiber in the ground that goes to homes and businesses. However, that copper and fiber weren't placed for internet; they were done so for cable TV. And because of all the M&A activity in the 90s when being a regional cable TV provider was good money (assisted by legislation they and their predecessors crafted in the late 70's to protect their networks), they had near national infrastructure in place to convert the signal from TV-only to the 1's and 0's we depend on for cat pictures.
Nothing wrong with that, except those pesky cable TV laws that prevented them from being competed against in cities. Those laws made it legal (read: mandatory) for cities to offer franchise agreements giving the likes of Comcast exclusive access to the residents. Now we are in a state where one provider (maybe two in a large city) provides cable internet. The same happened in the DSL space (different means), so now most cities are left with this for internet: One cable and one DSL.
That's it. Sure, TV can also be grabbed from satellite, both DirecTV and Dish, but they don't offer internet (and often bundle with DSL providers who haven't done an IPTV). For me, it's Comcast and CenturyLink, the Tweedledee and Tweedledum of monopolistic internet providers. The only plus side to the proposed TWC and Comcast merger is that I'm in one of the few areas they have already offered to spin off and sell to another company... so maybe I'll not have my name changed to offensive words when I call to complain yet again about channels not coming through, poor bandwidth, and the fact that HBO Go can't be used on the PS4 or Amazon Fire because Comcast is the only provider that refuses to allow their customer accounts the ability to activate it.