I live in a central European country and receive 0-2 spam calls per month. And that's because my phone number was used by someone else before (it's a company phone).
US has a lot of rich old gullible people speaking the same language. Central Europe doesn't, so it's not as cost effective to target. It doesn't help that you can hire a lot of English speaking people for pennies in India to staff the call centers.
Why is this such a big problem in the US?