Another limiting factor is that Motability joined forces with RSA some time ago to run a dedicated insurance company specific to it’s lease cars, with Motability becoming liable for financial losses incurred. The price and power restrictions help to reduce the historically calculated risk.
I used to think that, until I had a front bumper supermarket crunch (someone actually dented the front bumper 3 weeks before new car due) motability assured me it would not affect the gcb and RSA said not to fix it as the deal with motability is they own a percentage of the car for insuring it and the cost of repair would outweigh there cut.