This is fighting, you go until the ref pulls you off or you risk letting your opponent back into the fight. People who were "out" have comeback and won fights.
Watch Tennis or Soccer if you dont like it.
Its not as much about that, you can tell that the guy is out. Its more about wanting to cause a lasting injury. The fighters ive talked to all said they're trying to cause permanent damage because by fighting someone youre trying to take food out of their familys mouth. I understand the logic, thats why late hits, spitting on your opponent, and taunting KOed opponents shouldnt be punished.