Why didnt the Bear kill Leo?

Nope. Animals kill out of instinct with the intention being to eliminate a threat or to eat. Humans, for the most part, have beaten natural selection and evolution and thus have other complex motives to kill (sport, satisfaction, sadism, business etc.). Furthermore, animals rarely kill or attack on first sight simply for the sake of it. Almost all predators all the way up to bears prefer to run away upon confrontation unless they are hungry, threatened or have offspring to protect.

I feel like you didn't really comprehend what the comment you responded to was trying to say at all.

Having done my fair share of hunting, I enjoy game meat on my dinner table, you don't go into the forest without binoculars. Bears are usually laid back beast, unless fed, they usually avoid humans. However if you're in the woods in late October there is a tangible that you have to be aware of. If a bear hasn't stored enough fat for its hibernation it will look upon you as food. If a hungry bear charges you have only one shot before it tears you a new Arsenal. You have to shoot it through the heart, anything else and the bear is on top of your. And it goes for the richest store of protein - your brain.

As a hunter I've always eaten what I've killed, those that hunt for sport are degenerate cowards.

https://www.youtube.com/watch?v=uRiVkmiSiIU

That's what I heard, that if you 'play dead' after the initial attack the bear will often lose interest and leave.

When I was in Yellowstone I went hiking with a friend who had just done a ski season in the Rockies in Canada, and he says 'we have to buy bear spray'. Er, what now? So we go into a gas station, get our big old can of bear spray, and I'm reading the instructions in the car enroute. The below is from wikipedia, but you get the gist:

Bear spray is intended to be used to deter an aggressive or charging bear. A user points the canister at an aggressive bear and sprays the contents for at least 6 seconds. The recommended minimum distance between the user and bear is 25 feet (7.6 m). Using the spray improperly can have undesirable effects. Because the deterrent effect depends on the bear receiving a concentrated dose of spray, using bear spray on objects or clothing is not effective, and can actually attract bears.

I don't think I'd have the guts to wait for a bear to get within 7m of me before pepper spraying it!

In the movie, I assumed Leo's character would have knowledge of bear behaviour, it actually surprised me that he provoked it a second time.

It's too cerebral! We're trying to make a movie here, not a film!