I'm surprised by the magnitude but I can see why this would be the case. Working teenagers probably correlate with having parents who value work. Plus it teaches some valuable skills early on. An entry level job can throw all sorts of uncomfortable challenges at you, which you are expected to handle in stride.

I'd say there's a societal benefit as well, due to the empathy it promotes. Most people work very different jobs as an adult than they would as a teenager. Having more perspective on what other workers experience makes one more kind and reasonable in general.