I find this improbable. Just because you don’t see horses in the fields doesn’t mean they stay locked up in a 12x12 stall and never have any exercise. I hear the same thing lobbied at Saddlebred barns all the time and it’s not true. They don’t go out in the field, no, but they do get plenty of exercise and stimulation.
However, your comment was specifically addressing the 30 horses on 5 acre phenomenon, which is what I was referring to. On 5 acres, you don’t have huge fields TO turn out into.
I think what you’re seeing with those large barns that have huge fields is a resistance to having the horses get hurt in pasture accidents which is a very different kettle of fish. When a top hunter costs as much as my whole farm, I can see why owners bubble wrap them. I don’t agree with it, but I understand it. I can also understand the pressure a trainer is under to keep that horse bubble wrapped. They can’t show injured, and owners are quick to yank horses into another program if they think a trainer has been “negligent”.