I've been getting like 5-10 robocalls per day since I arrived in France. Based on this article, it seems the reason may be that my American carrier (T-Mobile) is better than my French one (Orange) at blocking spammers: https://www.nytimes.com/2017/05/11/smarter-living/stop-robocalls.html
@nolan T-Mobile does have a bunch of "machine learning technology" in their network to block spam calls. I guess it works?