It is, but not because they have a plan beyond it, though.
Cox/Time-Warner/etc. basically shook down Google for money a couple of years ago. Google backed down and the last-mile ISPs thought they won.
Google, of course, was extremely unhappy to painfully discover that there was insufficient competition if the ISP's decided to play dirty and block their ads. So, Google now looks at the ISP's as a pure, existential threat that they must neutralize.
So, even if the ISP's upgrade or get really cheap, Google doesn't care. This is about making sure that no company ever has the ability to cut off Google's flow of ads to the consumer ever again.
Google will roll out fiber even if it's somewhat unprofitable just to slowly squeeze the ISP's into obeisance.