There is A History there, though I've forgotten a lot of the details. Basically, there was a plant disease that was attacking blackcurrants, and so just when the US might have imported a bunch and made blackcurrant flavored stuff in bulk... they couldn't. Which is why Concord grape took over as The Flavor for things for so long.

And properly, those are "zante currants", a small type of dried grape, not just regular raisins.