imagine the following:

if someone weighing 60 kg climbs on your body and you have to carry that person a few meters, let's say you carry that 60 kg person for a distance of 30 meters, would you be able to do this every day and hours? I don't think you could, so how would an animal like a horse not be too much of a strain on the animal by submitting such a person to it? The problem is that we are normalizing something cruel, athletes are not carrying weight, I would agree if horses just raced without them having to carry weight. but people don't want to do that, they want to enslave the animal in such an inhumane way and they are happy with that attitude