Well.... Okapis and Pronghorns do easily get stressed out by people in game so there is an actual disadvantage in doing roam-free enclosures with these animals. I have a roam-free Pronghorn exhibit in my sandbox zoo due to a lack of deers and I'm really not sure if I would do it again, as their wellfare drops pretty often, until they hide and calm down again.
But there are a lot zoos in real live that make bad decisions. Sometimes because they do not know better yet, sometimes to attraczt more guests and because animal welfare is not high on their list. I'm glad that the game allows us to make mistakes or not be the best zoo owner in the world. For some the latter is just a playstyle.