Its amazing how many people are trying to rationalize this attack as due to some degree of carelessness on the part of the campers with no evidence to indicate it was the case.
Bears are opportunistic omnivores, e.g. they eat anything they can get ahold of and overpower - roots, berries, rodents, deer, even other young bears, etc. This bear just concluded that there was something edible and available there and took advantage of the opportunity for a meal.
Here they can not say it was a startled mother protecting her cubs...remember the bear bell joke ?
There are many cases of aggressive bears stalking, attacking, and trying to kill humans.
The media does not like to report these inconvenient truths.
Bears will kill baby deers, baby elk, baby mouse...anytime anyplace.