My personal opinion is simply, grizzly/brown bears (technically its all one species and includes Kodiaks, just the size varies) are opportunistic omnivores who need to FATTEN up prior to winter. They need a certain percentage of their diet in meat and animal fats. The further into fall you get, they need that meat and fat. If they can't scavenge it, hunt it, they will take it one way or another.
Not a good time to be perceived as a prey animal in their range at that time.
Timothy Treadwell (who goes down in history as one of the F@cking dumbest people ever) thought he was "one with the bears"...until they decided he was on the menu.