While its possible to live enough far away from anywhere else for this to be true, I'm not sure the majority of non-urban/suburban/exurban U.S. is any farther away from other places than parts of the Central Valley.
O rly?

Looking it up, it seems California's Central Valley has a population density of 155 people per square mile. It may be empty as compared to LA. But, there are 28 entire states in the US with lower population density than that! Basically, more than half the states are more empty than the Central Valley. There are five states (North Dakota, South Dakota, Montana, Wyoming, and Alaska) with less than ONE TENTH the population density of the Central Valley.
And, besides that, CA, as a whole, is a cultural and economic powerhouse. The Central Valley is the middle of somewhere, because CA is somewhere, in a way that, say, the middle of North Dakota just isn't.