My own thought on bears in zoos is this.
Bears may be seen as difficult as are elephants as they are perceived to need huge areas to move around in, of course to feed in the wild they need huge ranges to satisfy there daily needs, especially polar bears, who live in territories rather sparsely populated with prey animals.
To be a bit controversial, The same could - at a push -be said about wild wildebeest etc. Their food is more widely and regularly available of course, but they make huge migrations following the rains to feed on fresh grass.
Taken a step further very few large animals can live in small areas, for the need to forage alone. How many wild creatures go out for a walk for the hell of it? or to look around for the sheer pleasure of it? they go either to feed or patrol there territories and search for mates. Most if not all animals once fed just go to sleep,or sit down and start chewing the cud, animals are active in cycles not full time.
My clients all keep chickens, they have large fenced pens to forage in, but I still dump piles of leaves, grass cuttings etc and go in to dig over the ground so they can find worms. Other wise they just feed from a hopper, then sit around or half heartedly scrathch the ground. The leaf piles etc give them the all important stimulation and encourages natural behavior.
But their owners think that due to the large size of the runns they are happy. As I'm sure we on zoo chat know, space isn't everything.
Given enrichment and stimulation bears should be well catered for in zoos.