because all that right-of-way, pole-stringing, and digging crap for fiber is a PITA.
http://www.mercurynews.com/bay-area-news/ci_30221848/google-fibers-silicon-valley-rollout-is-delayed-while
"They said that Google was going to re-evaluate this whole project because they were thinking of going aerial."
Google Fiber wants to start testing wireless internet to homes in over a dozen U.S. cities
http://www.recode.net/2016/8/10/12427558/google-fiber-wireless-dozen-cities
Probably true
"Last month, Alphabet CEO Larry Page ordered Google Fiber's chief, Craig Barratt, to halve the size of the Google Fiber team to 500 people"
https://www.theinformation.com/articles/inside-the-battle-over-google-fiber