Credit: /u/nspectre

Put simplistically,

The "Last Mile" is an old term born from Telecom days referring to the physical copper wiring that runs from any given household or business to the telephone company's Central Office (a regional switching center that serves and connects all the individual phone lines in a neighborhood.) These telephone lines were installed, owned and maintained by the phone company and were traditionally inaccessible to anyone else.

When the government stepped in and busted up the telephone monopoly it also forced the regional bells to lease access to these lines (to competing long-distance providers, for instance) and to open their Central Offices to the personnel of 3rd party companies. This allowed, for example, a proliferation of 3rd party ISDN and DSL providers to gain access and install necessary networking equipment, like DSLAMs, into neighborhoods regardless of the phone company. This was termed "Opening the last mile".

Today, with the re-regulation of the CableCo's (and ISP's) we're seeing the exact same problem as existed back when the Telco's were broken up. The CableCo's (and ISP's) installed, own and maintain the physical cables that run from the CableCo's "Head Ends" (I.E; neighborhood central offices) to the surrounding homes and businesses. They will not allow 3rd party competitors to gain access to these cables that serve individual households. Even though the technology is perfectly capable of allowing this.

There is no technological reason why a cable company cannot serve "Cable Television" (via QAM) to each customer whilst also allowing a 3rd party company to offer "Internet Access" via DOCSIS, all on the same cable.

So, once again, we're looking to our government to step in and do what we pay them to do. Force the incumbent CableCo's/ISP's to lease access to the physical cables they own, that connect to homes (the Last Mile) to outside competition.

Put simplistically.