* Competition for mates: A male bear might kill cubs to bring a female into estrus sooner. Females are usually only receptive to mating after their cubs are independent.
* Infanticide: A new male in a territory might kill cubs that aren't his own to ensure that his own offspring have a better chance of survival. This is a common behavior in many animal species.
* Accidental encounters: In rare cases, a male bear might accidentally encounter and kill cubs if he doesn't realize they are there.
It's important to understand that grizzly bears are wild animals with complex social structures and behaviors. While these actions may seem cruel from a human perspective, they are often driven by evolutionary pressures and instinctual behaviors.