Free contact is honestly redundant in the context of modern day elephant husbandry. Aside from what are significant risks to the safety of those working with them, protected contact promotes healthy and natural social interactions within the multigenerational herd.
For the most part, it’s a relic of the days where elephants were kept in city zoos in elephants houses, where there outdoor area was at best, a small yard. By operating in free contact, elephants could be walked around the zoo, gives rides (earn their keep) etc. I recall a former Wellington keeper noting in an interview that while the zoo’s elephant house would be considered inadequate by today’s standards, the whole zoo was effectively the elephants exhibit by virtue of their daily walks.