According to a study from the U.S. Department of Commerce, a significant fraction of the US population doesn't use the Internet at home. In fact, 23 percent of all US households report that no one in the home uses the Internet at all.
ars technica, which has a chart in their article listing the reasons why citizens do not have broadband at home, notes that the biggest reason is a lack of interest, followed by cost. As the Commerce report indicates, "This means that a perceived lack of value or need was a more significant factor than affordability for non-use of broadband Internet services."