Certainly, fear and stress. In fact, the trauma suffered by wild animals subjected to capture and transport is well documented and sometimes fatal. Veterinarians and biologist refer to it as capture myopathy. There have been at least three confirmed mortalities from the 50 elk released in Royal Blue Wildlife Management Area in Tennessee this past December. Capture myopathy is thought to be responsible.
Wild animals are habitual creatures.
They establish a home range which they know intimately. The shock of a new environment may also contribute to capture myopathy. This is where those paradigms begin to clash. If there were a sign-up sheet or a volunteer list for elk that wanted to repopulate the Southern Appalachians, all would be fine. But that's not the way things work.