Why new cars rather than used?
I’m all for supporting disadvantaged people to overcome things (generally, not just cars), but not to elevate them to things that are luxuries for working non disabled people.
Largely becuase if you are the funder / operator of the scheme the vehicles you are supplying need to be a known quantity – reliable, safe, warrenteed. It would be too onerous a task, practically and administratively to make supplies of vehicles on the scale these schemes are operated and be able to ensure that the are suitably reliable and safe. Its more important for the costs of purchase, use and resale to be predictable.
That would be the same for any large scale providers of vehicles. Fleet buyers don’t provide their employees with second hand vehicles, car hire companies don’t rent out second hand vehicles, the ambulance service doesn’t buy second hand ambulances because used vehicles introduce too many unknowns into the system.