I'm fairly sure that I've heard in a TV documentary about Hersheys that the reason why US chocolate tastes so bad (or unique, as they put it) is because in earlier days, it was shipped around the US by rail in unrefrigerated boxcars in high temperatures, so by the time it got to it's destination, it was seriously past it's best.
People in small US towns across the US, being told that Chocolate was the height of confectionery in Europe ate it anyway, and got used to the taste.
When distribution got better, people complained that it did not taste the same, and so it was re-formulated to deliberately taste the way it does.
This could be an apocryphal story, but I believed it at the time.
What I found hilarious was a declaration on the packaging of some Peppermint Patties that came from the US that stated they are a low-fat food, which is true (only a very thin layer of dark 'chocolate' on them), but as they are about 60% refined sugar, the statement really is designed to mislead the US population about it's suitability as part of their diet.