What I don't understand is why it is such a prevalent issue in the US but not in Europe.

I've had a couple of French phone numbers over the past 15 years and I can't recall a single time I got spam call (though I did get an occasional spam text message with a shady link). I know my parents occasionally get some call but it's a small handful of offenders that keep repeating the same call again and again.

I don't think it's a technical difference as you can make call using IPBX/VOIP without too much trouble here.