I was wondering if there was any makes or models of vehicles that are on the Motability scheme that just never get leased
I would say possibly yes in cases where a manufacturer wants to be seen to be offering a certain vehicle/model on the scheme, but for commercial/political or other reasons negotiates a stupidly high Advance Payment that only someone insane would pay.
Thus, they are seen to offer the vehicle but are almost sure no one will buy one.
A case in point may-be the current Vauxhall Astra Automatic with the cheapest DLA/PIP/AFIP Advance Payment being £1399. Compare this Advance Payment to the equivalent Peugeot/Citroen automatics from the same company (PSA) or even a competitor vehicle such as the Ford Focus etc.
It is obvious that PSA don’t want to sell many (if any) Vauxhall Astra automatics on the scheme as there are so many much better value automatic vehicles for much less advance payment.