Give all racehorses a good retirement when feasible

According to someone I used to know who used to work with racehorses, a lot of ex-racehorses end up being slaughtered when they are no longer useful. In fact, in 2011, the number of horses and ponies slaughtered in England, Scotland and Wales rose to 7,933, a 50% increase from previous years. That’s 7,933 horses and ponies that likely had feelings, many of whom probably could have gone on to live out the rest of their time with us in green fields and stables, being cared for, played with and given treats by people who love and know about horses and/or ponies. Yes, some of them may have been ill and/or injured and not able to cured or helped, but would it not have been more humane to have them put down by a trained veterinarian using lethal injection, at the homes of the horses/ponies or even at a veterinary centre?
I understand that there may be some cases in which the horses are badly injured and/or ill and can’t be cured or helped, and then it would be more humane to have them put down. I also guess that, maybe, there could be some horses that are unsuitable for such retirements due to incurable behavioural issues, but I would like to politely ask for a law that would require all healthy/treatable, adoptable ex-racehorses be given good retirements at the end of their racing lives.
Thank you.