OK, “CSI” has been on for over a decade and this just hit me while watching “Las Vegas” reruns this morning. Why doesn’t “CSI” use the term "Metro, " short for Las Vegas Metropolitan Police Department (LVMPD)? If I remember, correct me if I’m wrong, they say “LVPD” or "Las Vegas Police, " or “Las Vegas Police Department” The show “Las Vegas” uses “Metro” a lot.
Because “Metro” is ambiguous and can refer to any metropolitan area, while CSI Flagship does not have its city-identifier in its title.
Maybe when they wrote the pilot the writer wasn’t aware of the proper name of the police force in Las Vegas (LVMPD, as you say), and now they’re stuck with it for continuity sake. Or they chose a fictional name on purpose.
For awhile I always thought it was odd that the CSI folks answer to the Clark County Sheriff, but that’s the accurate state of law enforcement affairs in Vegas.