The arrow cuts through the blood vessels and nerves. A bullet blasts it's way through. I heard of a guy who killed an elk with an arrow on a really lousy shot - he hit it in the lower leg. It bled out and he recovered it several miles away. I doubt you'd find most animals that badly hit with a bullet.
I've seen animals hit in the ham bleed out rather quickly when the femal artery is crushed by a bullet
