Whenever I read something weird like this I always need to remind myself to mentally add the quantifier "in America". Salty licorice is very popular in a number of European countries including mine (NL).
So it's definitely not just Europe.
I'm American but was so intrigued after finding it so unpalatable the first time I encountered the salmiak lakrids despite people clearly liking them. I was keen on finding out if it was just a matter of getting used to it.
Now I actually enjoy it and like it. I just still can't handle letting the stronger ones dissolve all the way. It's also very fun to give other Americans to try (I warn them) and see their reaction.
When they say "betcha can't eat just one" that's not a motto, it's a taunt (or a scientific fact, depending on your perspective).
That's about as sensible as saying "Not many people like salty popcorn".
Black licorice is already a contentious flavor here, throwing a big pile of salt on it (however delicious that happens to be) further reduces the audience)
And yes, it's great!
(I learned about it myself during a photo scavenger hunt in Seattle in college. I'm still amused by the photo from that where the rest of my scavenger hunt team was dying from taste, and I'm the only one enjoying it. There was a well known wharf candy shop we were directed to as the easiest place to buy it and get that photo op [and they were used to and amused by college kids making the stop].)