[washadjeffmad]

A university campus is like a microcity with thousands of people, its own economy separate from the surrounding area, facilities, and rules. Instead of sending off reports and requests to city police (and how many students, staff, and faculty are locals, again?), they can have a single, centralised, limited office to handle public safety and policing.

Put another way, it's so everything that happens within the university doesn't eat into municipal or county time and resources, but they can still interoperate with some parity.

Look into the Clery Act for more.