That's almost entirely a myth. Along with the myth that most of the cheese sold in the US is "American Cheese" or "cheese product." These are fantasy lines of attack on the US for people looking for an excuse to bash.
Here are two more of those myths: the US only sells mediocre, watered down beer (that one has long since been destroyed, it rarely gets used now); and the US doesn't make any good domestic wine that is competitive with eg French wine.
The average Walmart (a mid to lower tier grocery) has a large, normal selection for real chocolate of all varieties (including European). Typically they will have a large half aisle filled with real chocolate candy products to choose from.
The US is the world's largest market for real chocolate.