It's not a matter of terminology, it's an overview of the political spectrum. The discourse over what's considered the norm in the United States has skewed so far to the right today, many Americans don't even understand what "left" means anymore. The term itself has become a bogeyman, used by politicians and special interest groups to scare the populace into supporting them.
Ironically, America generally isn't as "rightist" as it may appear. Surveys show that many policies that would be considered "leftist" enjoy wide popular support in America in and of themselves: greater tax contribution from the rich, affordable health care for all, more support for small business, lowered tuition fees for college students, affordable children's daycare, and the like. It's just when those policies get lumped in with the bogeyman that people start to balk.