We keep getting this discrimination card thrown about. I agree whole heartedly that it sucks, however… they are selling the car to a private buyer on the basis of higher sale price, not your disability, age or any other protected characteristic. Motability sales are not a forced provision and dealerships have no regulation mandating their sale to any customer who asks. It’s entirely their choice.
I tend to ask if they can sell an in stock car via Motability, I waste no further time or energy pursuing those dealerships who choose not to.