- 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.
I have, in fact, gotten periodic spam calls, though only once or twice an SMS - usually trying to solicit me about my car's insurance policy having issues (I do not own a car).
I sort of wish I could convince my Android phone to treat all calls to my direct number from anyone but GV as spam, because I have never given that number to anyone.
Monetary or social costs were both asymmetrically in favor of the receiver because a long-distance call was expensive and a local spam call would eventually incur a high social cost (either in the innocent case of teenage prank calls being figured out by parents or the less innocent cases where the police or phone company might need to trace the source).
There are too many nuisance calls, there are too many people (and businesses) falling for scams, and there seems to be nothing telcos or governments are willing to do about it.
It's pretty much the same thing that's happened to Usenet and Email (and is now happening to the Web as well). John Gilmore's lament about crackdowns on open email relays is heartfelt, but ultimately naive. If I'm remembering correctly (and I'm probably not), it ran something like: We created a way for anyone anywhere in the world to talk to anyone else, and it wasn't an accident. The problem is of course, bad actors, and lowering costs means enabling vastly more bad actors.
Figuring out how to impose highly asymmetric costs --- and not necessarily financial ones --- on unwanted communication attempts, will win this.
The technical problem is reasonably straightforward. Generating widespread adoption is the real challenge, IMO.