Unlike most other counties US does not have much in the way of Internet broadband policy. Each company is free to optimize its business any what it chooses. This tends to favor short term profitability vs long term growth. Almost all the cost of delivering Internet access to in the First-mile. If First-mile providers decide not to upgrade their network things come to a grinding halt.
The other problem is Cable companies and to a lesser degree Telcos are worried high speed access will undermine TV offering. Once First-mile speed is fast enough the door is open to IPTV undercutting first-mile provider's lock on that service.
May want to check out some of Andrew Odlyzko's papers on the subject.