I don't think horse racing will ever be banned(maybe until the market for it dwindles or something), they've had a lot of chance of banning it but instead, they put stricter regulations on how the horses are treated.

I remember reading somewhere that the reason they just kill the injured horses instead of trying to rehabilitate them to its full health is that it is expensive and even if the horse has been recovered to it's full health there is no guarantee that it could perform like before.