Have you ever had the nasty experience of finding some poor little dead creature slap-bang in the middle of your kitchen floor? Or, worse yet, has your 'oh so innocent looking cat' dropped a mutilated prey right at your feet and acted as if you should be pleased about it?
"So OK, cats are natural born hunters, but why do they have to bring their catch home?"
There is more than one theory on this, but the most likely explanation is that your cat views you as an incompetent kitten who needs schooling in the ways of hunting. Spayed females are the most likely to bring home their catch. Kitty may be deprived of the ability to reproduce, but she does retain maternal instincts it seems.