The wild offers more natural structures and temperatures that keep animals adapted to their surroundings. However, in captivity animals tend to differ from their wild counterparts. For one thing, the wild cultivates an animal's hunting skills but, when or if they are releasing into the wild, they do not know what to do whereas they have been sheltered their entire life. They don't know how to find natural structures to keep warm in, what places are safe or even survival strategies. The conditions in the wild teach an animal to survive while the conditions from man-made structures just give them an easy survival.
Hope this helps and have a nice day.
-R3TR0 Z3R0