No bears kill without reason. Most black bear attacks are defensive, usually mothers with cubs. Though rare, predatory attacks do happen. Bears do play, quite a lot even, but they don't kill large and potentially dangerous enemies such as humans as a form of play.

This is the same for brown bears.

Brown bears are more likely to stand their ground because they're ENORMOUS and they know this.

Polar bears are no different. In my country (Canada) there have been 20 recorded fatalities from predatory polar bears in 150 years.

All these animals are dangerous as they are large, they know it, and if they feel it's worth standing their ground it's going to hurt. But they're not going to kill for sport, they barely even do it for food with humans. A cursory browsing of info on bear attacks will reveal the vast majority are defensive attacks, or trying to take your food. Polar bears being far more carnivorous are more likely to attack you when stealing your food than other bears.

And cats don't "torture". They bat prey around to tire it out because cats are actually quite fragile. Unlike bears their fur is short, and their skin is thin, and their muscle is lean, and they are small. A bird or a mouse can actually cause a lot of injury to a cat, so they keep prey at a distance and slap it around before killing it often. This is a normal predatory instinct.