Any new entrant has to build out a cable plant to reach subscribers and capture enough subscribers at a high enough density to make it worthwhile. The only company that's even trying at this point is Google.

2. Most of the larger markets are in densely populated cities, which makes laying infrastructure even more difficult (there's a reason that Verizon rolled out FiOS to suburban areas rather than urban areas).

3. If your 'value added' is something that the ISPs can easier undercut to drive you out of business (e.g. expanding bandwidth caps, increasing speeds), then your business proposition becomes even shakier.