They'd be nickel and diming the other agencies. If you think otherwise, then you're simply wrong.
All the local PDs have, at most, sufficient personnel to street 3 shifts, 7 days a week. They street more patrols on Saturday than any other day of the week. Anybody who works a Saturday football game at Rutgers is going to be unavailable to their own PD during a critical scheduling period.
MCSO, on the other hand, has a total complement of 180. Unlike the local muni PDs, they don't street a normal shift on weekends - their normal operational shift on Saturday is 6. That leaves plenty of people open to do outside work.
So if you throw out MCSO, then you have to get 60 guys, 2 and 3 at a time, from a minimum of 20-30 agencies. You're now introducing a considerable logistical and C&C challenge - the most obvious being that the MCSO guys all have the RUPD ops frequencies on their radios and none of the other local PDs do, besides New Brunswick, Piscataway and Highland Park - all of which are represented as part of the 212 total.