Not sure why are you singling out US here. People all over the world like "ecsotic foreign" stuff and pay premium for it. Starbucks has 2000+ stores in Europe despite having a lot of smaller (and sometimes shittier) smaller shops. Same as in US.
The truffle flavor is no different from the fake "college t-shirts"[1] that big pseudo-american chains like NewYorker[2] sell all over the Europe.