[ocschwar]

Historically, land-grant universities predate state police forces. In fact, in most of the US, state police forces are there primarily to enforce traffic safety laws on the highways, because out in the countryside, drivers cross county lines too quickly for the sheriff's police forces to fill that role.

Also, regardless of the formal chain of command for a university police department, the licensing of police officers (i.e. certifying someone as eligible to wear a badge) is a state matter. A university cop doesn't draw his salary from any government, but he can still get his badge taken away by the state if he misuses it.