[dredmorbius]

It's probably a number of factors:

- The US remains relatively high income / high wealth. Especially among the more vulnerable senior population.

- The regulatory environment in the US hasn't been successful, or much interested from appearances, in taking on spam.

- Uniform language. Virtually the entire country speaks a single language, English. That's roughly 300 million targets (minor children generally wouldn't count). The largest single European nationality would be Germany, with a total population of 84 million. It's not even possible to necessarily presume an entire country speaks one language, as with Switzerland. And though computer-generated calls are increasing in prevalence, most still use human speakers.

Effectively, it's opportunity, mechanism, and logistics.

But as costs fall and voice-processing (both comprehension and realtime generation) improve, I'd suggest increasing your vigilence around telephone hygiene.