system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is Google fiber and why isn't it in many places?
gpt
It's Internet (and TV, but not phone) service provided in a few cities so far. It's provided over fiber optic cable, which allows very high speeds. Other providers use fiber optic cables too, but they are either not used all the way to the end user's home (e.g. using coax copper cable there), or they simply set the speed lower than technically necessary. All that user data has to go to / come from somewhere, so it's more expensive to allow full speed.

It's not in many places because it's very expensive to install fiber to every home and business in an area. The fiber itself is much less expensive than the installation - planning, digging, permits, etc. Think about how much it would cost to dig up the street near a single family house, then branching off and installing a cable into the house. Then multiply that by the number of homes in the neighborhood or city.