Why do some foreigners think every state in the USA is like California and New York?

TV                           

Because they probably only visited California and New York. There is not much of any other reference to go by until they actually visit the other states. Plus TV and films doesn't help much since the concentration tends to be in California and New York which is where the studios is located.

Better to just inform them of the differences.

@F: I always though you guys were all crowded in Islington and wore bowler hats.. but that is just me. ;-3

@Artemisc: About your uncle, you should of made this into a personal project. Drive the 8 hours up and make him ride the 8 hours back without bathroom breaks and playing "The Liberty Bell March". Serve only coffee and bran muffins. :-)

Because 99% of people are plain stupid in all countries and just don’t think about anything outside of what they are in films or on TV.

Americans are probably the worst people for this believing everyone in England lives in Victorian London.

Because that is what they hear about the most. They make the assumption all big cities are like NYC or LA. They don’t have the experience or knowledge to know about other states.

I am sure all of France isn’t like Paris, but many tourist may think it is. 

The same reason many Americans think Canada is covered in ice and snow all year and that we have moose wandering the streets everywhere. They only know what they have seen on TV and the movies, haven't bothered to find out more, and haven't visited.

Because the US media generally covers the nation as if it's all L.A., NYC (and DC). 

CA, NY or Texas.  A lot of Europeans think we're all cowboys.  In my experience, the hardest thing Europeans have to understand is just how spread out everything is, and how lousy our public transportation system is. I live near DC, my British uncle was coming to visit and wanted me to pick him up at the airport.  In Detroit.  He didn't get that it was about an 8 hour drive one way, but out was $100 cheaper. As first, he didn't believe me that it was that long a drive as they "looked close on the map".  This was before googlemaps. Needles to say, I didn't agree to pick him up in Detroit.  

Perhaps because that's the only places that people outside the US have seen (eg in films etc).

Just like many US citizens may think everywhere in France is like Paris.

cause they havent been to the other states

maybe cause they havent been to the other states