> The fact that places like Seattle, suburban Los Angeles, rural Maine, most of Nebraska, and Miami are in the same country seems almost absurd.

Why? I can drive an hour away from where I currently work and experience more linguistic diversity (in terms of dialect intelligibility and actual language spoken) than I can in almost any region in the United States. And this is not, in any way, unique to where I live. Drive an hour outside of Taichung, Abu Dhabi, or Bangkok, and compare the differences in how people speak, live, &c. against Atlanta and rural Georgia.

The truth is that America is incredibly, incredibly homogeneous.