I only heard this recently and it blew my mind (ok I'm easily entertained).
So apparently in the early 1900's there was some fungus outbreak that was having serious effects on Amercian crops and it was believed that Blackcurrant's were the cause. As a result the plant was completely banned across the whole of the US.
Apparently the ban has only been lifted in the past few years but because they're just not used to the taste it hasn't caught on as a popular flavour.
Seriously we love this stuff in Europe!! Can you imagine never knowing the joys of Blackcurrant Ribena??