I'm not talking about that. The government waives multiple taxes for the scheme. Off the top of my head, no VAT on the car purchases, no luxury tax on vehicles worth £40k+, no insurance tax, no VED (road tax).
The scheme has cost billions in lost revenue and it's the only reason it can exist. The exact accounting is up for debate because it's complex but nonetheless.
There are / were no £40k+ cars available on Motability
Can't find it now but there's a breakdown of the cars supplied somewhere and even when small BMWs etc were available very few people chose them - most people chose smaller average cars
Motability also plays a huge role in priming the used car market in the UK - without them there would be less choice and cars would be more expensive