I see where this assumption comes from, but scraping the personal info off a phone is a thing, and "random thieves" might be the minority when it comes to stealing and reselling phones (at least in europe or asia they are rarely random. It don't know for the US).

I haven't heard of it recently, but a few years ago there was a story on phone operator temporary staff that would offer clients to move their contact info from their old phone to the new one (it's a completely legit service) and keep a backup of the old info to sell it. The price for an entry was something like 2 cents, but data would be sold by batches for about 700~800 dollars.

I didn't find any quick resources in english, just for the numbers there was this piece by trendmicro (to note, they are of course biased to make the number a littre bigger) http://blog.trendmicro.co.jp/archives/4828