The county operates the busses. Right now, I think there's no reason for them to move to the existing Type II/SmartZone system as it's going to be replaced (hopefully) in the next year or so once Motorola figures their life out and delivers the system as they promised a whole 11 years ago. Once that happens (shooting in the dark here), it's possible the busses could move to that system since it has increased capacity.
If what they have right now with the VHF system works for them, no reason to spend several million dollars on new subscribers just to switch to that system unless they get some sort of grant to be more connected to public safety.