Because in the US, planning and zoning falls not under the fed, not under the state, but under the city/county level. In Korea, the fed basically said, nope, we're going to approve this everywhere.
Why do you think google fiber is so selective? Because it is a regulatory nightmare for google to get the unbelievable amount of paperwork done for approval. Even for cities that want to work with google, a lot of them still aren't really able to due to the amount of bureaucracy and red tape required to pass planning/zoning committee muster for each county/city/etc.