I believe JLR at one time, was one such manufacturer looking to offer similar to what the scheme does however, it never materialsed into anything. Any such competition would require a similar DWP setup as Motability does, where the mobility component of the benefit is paid direct rather than go in a claimants pocket and rely on them paying every month, which would leave the competion wide open to non payment, chasing payments etc, which would prove costly. Therefore for the competition (if there is), credit ratings will be at the forefront, even if manufacturers were prepared to do favourable deals to the disabled. There is also further complications of VAT outside the scheme.
On the other point, I wholly agree it is ludicrous that the government bowed to pressure and Motability, didn’t put up any meaningful fight to secure the longterm premium brands on the scheme, which would command a higher sale value than an equivulent Ford with the same AP/value or do anything to correct the public perception of “free” cars