Horses poop a lot. A lot.
I had to search about and it's indeed a lot:
"it is quite normal for a horse to poo (defecate) 8-12 times a day and produce anywhere from 13 to 23 kilograms of poo a day."
More than pooping a lot, they literally cannot hold it. Humans don't poop that much, but imagine if everyone just did it on the floor at a moment's notice regardless of where they are
So Red Dead Redemption 2 was actually realistic? I always wondered why the horses were pooping all the time. It's because of AI.