Makes sense to me. It would not take a smart person to realize how dangerous riding a stud horses is.
I have only been injured by one horse, and it was a young stud.
The next day he had them whacked off.
Apparently horses were quite a bit smaller than today's models back during the early period of domestication.
They got bigger through time until finally there were horses with the capability of carrying a rider.
Even larger horses were bred, and the Middle Ages saw a horse big enough to carry an armed and armored mounted knight.
Obviously the Chinese went right to the question of getting bigger horses. That meant the smaller males were gelded and then put to work pulling wagons and chariots.
In the end all of them were roasted over hot coals to feed the troops.