You nailed it.
But many people do not care about it. They just want to have fun and money at the same time. I am not sure what goes on in the mind of horse owners. Do they really have soft heart? I doubt that.
Let alone horses, considering cock, spiders, and dogs, if they just want to make fun, they will make everyone fight just to make something to bet on. Maybe they cannot resist the old habits they have and don't care about the animals after all. When I saw the no-choice in the eyes of those animals, I translate them as cruelty and those people involved in this somehow don't have any hospitality towards those animals when they lose the game.
This becomes quite difficult for some people to accept because they think that there is still a lot of exploitation of animals that is still going on and maybe things like this are not considered as exploitation because they think this is a natural thing when compared to other cases of torture.
even though on the other hand things like this might be minimized with the smallest things but indeed this will also be a little difficult to happen considering that things like this are commonplace in some areas