That reason is because Hersey chocolate was the first chocolate the common American could afford and the processing method that Hersey used to produce it would create butyric acid from the milk. Now they add it back in because customers complained when they refined the process.

While in American, in right there with you. Aldi fortunately imports a good selection of chocolate so not all of us have to suffer.

Oh my God is that why I taste vomit if I eat a Hershey's bar then drink a glass of water

A colleague came back from the US with a big back of mini Hershey's flavours. Most were ok but I legitimately thought the standard plain flavour had spoilt.

Growing up and living in the US and then accidentally learning to taste the butyric acid after tasting chocolate without it made me sad :(