It's not the radios, it's the portable/fluid nature of the equipment and operators.
Townships don't tend to invest in portable fault tolerant systems. Though post 9/11, a bunch of DHS money has gone into portable repeater trailers with powered extension towers on them.
The trouble is, in the case of a major/mass disaster there is higher potential for losing a singular resource that was the backup. With hams, you have people all over with their own radio equipment that is portable and often easily adapted for mobilized operations.
The whole concept is strength in numbers for redundancy.
In our local RACES we have radio equipment stashed all around the county, in addition to all our own equipment. Even if a severe hurricane struck the area, the likelihood is very high that a portable field ops station could be assembled and on the air in short order.
Locally, our amateur repeaters stay up on the air much more often than the municipal machines during severe storms and power outages. My local town's system goes down all the time due to power issues while my local repeater is always up.
Also municipal systems don't have the extra-regional capability that we do with HF NVIS comms (40m 75m). So if an even was severe enough to knock out telephones and cellphones, we would be the only ones immediately available for this capability.
Yes there are military and government units that have all of this and much much more with satellite links, but it takes them days to get on location. RACES are who provide the initial communications capability until being relieved by other resources.
Hams operated at ground zero for many days because comms were so constrained and comms coordination was so strained. There was equipment all over, but the agencies didn't have it running properly until days later.
Most cities don't even have a significant staff of radio techs capable of managing the actual repeater configurations...that's all done by contractors now. Towns may have a few guys that program portables, but those guys don't know how to whip up an improvised repeater, nor do they have a bunch of them lying around.