It's pathetic to know this fact.
But, in fact, Horse Racing has always become one of the most favorite bettings in the world, moreover many big gamblers from rich people love doing betting in this Horse racing. So, this may be very hard to stop or ban this betting. You know, big business is there and we may fight with many rich people with high powers in the world, or in each country.
Those deaths are logical enough. The horse may be also treated as a human athlete who must also do some diet that will make their body healthy and fit in every race, high periods of training every day, and other pressures that of course got by the horses.