Experience isn't a hierarchy. Having a PhD doesn't make someone good at tasks they've never done before.

This ignores the real reason that over-qualified people are often skipped for jobs: They are never interested in staying at that job. It's always something temporary until they find the job they really want, which could happen in days, weeks, or months. They probably won't give 2 weeks' notice because they don't care about their references in the retail industry, meaning you're emergency short-staffed and have to repeat the hiring process all over again.