That a lot of info isn't applicable to the rest of the world. You'll constantly find talk or recommendations of products not available elsewhere, or people talking about a law as if it was universal, the disgusting flood of USA politics, and basically a list so long it'd reach the moon. It's an infinite cultural tsunami obliterating any sign of diversity or useful information for the rest of the World.
^ tldr:Their lack of general knowledge about rest of the world.
I lived in US for a while, in San Francisco, one of the most educated places in whole country. I can understand what doacid mean very well, hard to explain though.