[d_sem]

More likely the cultural practice was not passed down after the massive change in food preservation about 125 years ago. In the United States, fermentation was a universally practiced method for the pickling of vegetables. This practice has been so reduced that the word "pickle" now only refers to cucumber preservation.

[willy_k]

I don’t agree that the word “pickle” has been reduced like you claim. Used as a noun, it is only applied to pickled cucumbers. But it’s used as a verb is still very common and the average person understands that many things can be pickled.

Although if you were to ask them to guess at the etymology, you probably would get a lot of disappointing answers.

[jimnotgym]

I think the big difference is sauerkraut is pickled in brine, resulting in fermentation. Whereas all the pickles I grew up with in the UK were pickled in vinegar, which doesn't produce fermentation. Pickled onions, eggs and beetroot come to mind