The purpose of Google Fibre Here's the point:
When Google created their browser, Chrome, it stated purpose was that the state of browsers at the time were abysmal and Chrome would push other browser vendors to create better browsers to help move the web forward, technically. This has happened.
Today, Google's stated purpose of building their own network is to show what can be done so other providers will improve their service to help move communications forward. This will happen.
Google's purpose for doing both is to make the web and TV better so they can sell more ads (whether you also believe in their love of technology or not).