Find that really shocking. That's over 150 a year just in the UK. Just googled a bit about it and it looks like you can treble that when you take into account deaths that don't occur during a race.
How is that allowed to happen with seemingly so little opposition?
For one very good reason - money. It should be banned but Cheltenham is even worse.
The national is a disgrace as it allows far too many horses in the actual race many of which are totally ill equipped. It's far too long and many get withdrawn during the race and are shot afterwards.
The notion they are treated like kings during their career is crap as well. Most are destroyed or abandoned and all are condemned to 22 hours a day in a box rather than their natural environment.
It's a brutal brutal industry and the notion that owners and jockeys care about the horses is bollocks. They are generally a very unpleasant bunch.