I think available cars on scheme is driven by importers/manufacturers decisions. Apparently Motability negotiates quite aggressively to get huge discounts. Some companies like Tesla, Polestar and Genesis have online pricing model hence will not budge. I expect more (EV) deals towards end of the year when ZEV mandate starts to bite (Ford, VAG, Toyota?)
When we got our first Motability car 12 years ago the dealer gave us the original invoice by mistake. Retail price of the car was about 27k including VAT and Motability paid 16k only after VAT and discounts deducted.