Knowing that this has gone on for decades little will ever change I am sure but a bit of advice.
our last 4 cars came from stock as we are not patient waiters of cars. That said a couple of things firstly be prepared to travel always say will you sell this to Motability up front it saves wasting your time, then try and order over phone saves what can be two long trips if far away, and if it’s a big franchise one dealer can differ from another. Our current car last year we found four at one franchise spread over 4 dealers, but 3 refused and one said yes so I think sometimes it’s definitely a local decision to say yay or nay. But I can recommend chasing cars if you have the time.
I am the carer / driver for my wife who cannot drive due to disability