1. There are too many 'tin foil hat' people that will protest against any fiber cabinets.
2. Seattle City Light / CenturyLink jointly own most telephone poles in Seattle.
3. Comcast / Wave Broadband already have coaxial/fiber networks strung on those poles.
4. In the case that some poles are rotted and need to be replaced, the money for those poles will have to go out of Google's pockets (and trust me, thereare plenty of those poles that should've been replaced a long time ago.