Because they have learned on trained horses. Some young trainers have not had to manage livestock farms dealing with animals on their terms. The SRS has their breeding farm at Piber out in open country, not inside the city of Vienna where the shows are. At the outer farms of the stud, they manage the mares, young stallions intended for further training or for sale and all the young stock.
As much as people want to treat horses differently than a farm animal, they are domesticated livestock. People need to respect the animal and acknowledge they have personalities, just like people. Some are higher energy and need turnout, others are willing to be “couch potatoes” and hang out in a pasture or stall eating hay.
I was at Strömsholm, Sweden over a summer when the king/queen’s horses were turned out for summer vacation.