I don't think black bears are that big - although a little research shows you are right.
Still, people keep lions, wolves as pets. I'm pretty sure an omnivore wouldn't be any harder to rear than those! Bigger animals are often less nervous, IME, so easier to work with.
I grew up around race horses that would frequently 'test' you; one of them had killed a stable hand at the previous stud, so not really nice animals at all. It's all down to the animal's nature, really (and I have no idea about bears). Male chimpanzees seem to be the most impossible to have as pets.