Guess they wanted a bit more power to their rifle rounds, although a 22LR will do the job if you aim it right. If you're just aiming anywhere or in a particularly well padded area, you might want to up your round power. For small game, a 22LR is all you need, for larger animals, you might want to go up in size.
If it's for self-defense, well a 22LR will do for anyone able to place a good shot; in fact I remember an old story told to me by bunch of doctors, who claimed in terms of internal damage to head and enclosed cavity inside of a body, the 22LR did far more gruesome damage that was visible, because the round would bounce around and turn anything inside into mush, since the energy of the bullet wasn't enough to exit out the back and would constantly ricochet inside the skull or bones. Needless to say, the images they showed were horrifying.
