I dunno, I don't really think we're that far behind. It may honestly be a different lifestyle approach. The US is a very active-lifestyle oriented place, even if we are pretty chubby these days
Plus, it's a lot harder to coordinate things amongst the layers of government that are set in place to govern 300 million people. Some places are more tech-oriented than others. Plus...we sure as crap have to lay down more wires and build more cellular towers than South Korea does...
...and we're busy launching satellites for, y'know, South Korea, Japan, Europe's communication infrastructure.