I've been rejected from jobs because I was over-qualified. Then I got accepted to one, which turned out later that I was over-qualified for that one too. I did get bored, I felt like the job wasn't a good match for my skills, and I went looking for a new job.
So the concern is indeed very real and can cause unneeded churn for a company.
So the concern is indeed very real and can cause unneeded churn for a company.