We used to buy our own cars and put the Motability money in the bank, but that was through personnel choice. Then you have to look at people who live in cities like London, there is a good transport system and driving is a nightmare,(I have never lived in a city or London).
It is not compulsory to spend you Motability component on a car, it there financial to get you about.
Unfortunately I have suffered a brain injury and occasionally I get confused and often say the wrong thing.