Bears don't neccisaraly hibernate in captivity. They do this in the wild because food is rare. When feeded redularly in a zoo, they often do not hibernate, as it's stressful for the body to do so. However, they often have less of an apetite.
Some zoos give their bears less food in winter, so they hibernate. It comes from an old belioeve that the bear needs it, I guess.
However, pregnant bears also hibernate in captivity.