I have seen many engineering departments want professional engineer registration. Why do they care?
This is because, in the U.S. as in many other countries (like Canada), Engineering is a regulated profession, like medicine and law. To call yourself an engineer, or to perform certain 'engineering' tasks, you need to be accredited (or registered or ..., name changes by country) to do so.
They care for the same reason that they want lawyers that have passed their bar exam to teach law, etc.