What ever happened to modern technology in that less is more. Why couldn't they all run from one antenna?
Different antennas for different functions and frequencies. And, while it's technically possible for all the radios to use a single antenna, it wouldn't be very efficient or work very well. Sort of like how it's technically possible for a truck to have only one wheel instead of four. Not very efficient and it probably wouldn't function very well as a truck.
Also, the truck is two complete radio stations, one in the cab and another in the back, and they can work independently of each other. Each station has both VHF/UHF equipment, as well as full HF capability. So, for example, while one operator is in the cab taking reports from other operators at a disaster site, and passing them on to the state emergency operations center, a second operator can be in the back transferring medical data via digital packets to another station thousands of miles away.
On the whole it makes for a very robust system, with inherent backup redundancy.