Because, I assume, you aren’t abusive in your methods! If you decided to employ some more unpleasant tactics you would end up with an obliging horse, but I assume you’re nice and actually care about him so won’t ever do that.
You really didn't read my post did you? If you force my horse to do anything, he fights back. If I did use abuse on him, it would not work. He used to bolt at the sight of a lunge whip because he had clearly been hit with one a lot and wrongly. Its taken me well over 2 years to gain his trust that I won't do the same and for him to react sanely with a whip. He still panics sometimes, and he cant handle it with anyone he doesn't trust.
Anyone is naive to tar the entire sport with a few bad experiences. We should cancel dressage too based on that idea, considering the people who over tighten nosebands, ride the horses badly, etc. But then you have people like Carl hester who do it right and beat them. The idiots abusing their horses still havent realised they should do the same as him to achieve the same results.
Then you've got your average riders. Where do you start there? How about the overweight riders getting on their horses and actually making them go lame? The ones starving their horses because they can't handle them? Or worse the ones over feeding, over rugging and thinking an obese horse is normal?
The majority of racehorses are well trained and very well looked after. I can't say the same about the majority of average horses out there owned by your average person, not in racing or high levels of competition.