 Cats are not as social as dogs. They groom each other and will sleep together, but that's the extent of their interaction. Petting is not an instinctual behavior for them, it's something we, as humans, have domesticated them to accept. So it's kind of understandable if they seem to find it annoying. Cats most commonly bite us to tell us they want to stop interacting. Cats have sensitive nerve endings on their bodies that can lead to them becoming overstimulated. If you miss other signs they want to stop interacting, they may resort to biting you.