How far do you think a hand held battery powered radio can transmit it's signal? Unless you are talking about a HF radio using skywave propagation (to include some maths & carefully positioning an antenna that might be several meters long) it won't be very far, especially in a city or rough terrain. The benefit of having a vehicle mounted radio relay system means that it runs on vehicle power (or a generator) and can carry a lot more antennas. Radio retransmission teams who do exactly this with vehicles fitted for this exact purpose are prevalent in the military, most units will have several of these teams/trucks permanently assigned, and if not, their local signal unit can lend them.

I'm not arguing with the rest of your post, I'm sure there is way more fraud, waste and abuse then we can imagine going on. But the laws of physics still apply and if you want transmit a signal far, you need a power source bigger than what people can carry. Even a vehicle mounted and powered radio wouldn't be able to transmit 10-20 miles unless you were sitting on top of a hill in otherwise perfect conditions.