An additional reason could be how they find they prey. I’ve read that most of the time shark attacks are somewhat accidental with the shark biting to find out

An additional reason could be how they find they prey. I’ve read that most of the time shark attacks are somewhat accidental with the shark biting to find out what something is, but not continuing the attack. It could be that the echolocation abilities of toothed whales provides them with a superior ability to discern a human from their typical favoured prey and they don't make mistakes. It would be ambitious for a dolphin to kill a large animal like a human and that’s since that’s not their typical hunting behaviour, I can understand why dolphin attacks are not common. On other hand an transient orca would often eat human sized animals. Even if I’m right that echolocation would allow an orca to discern between a seal and a human, why wouldn’t they give the human a bite to see if they tasted any good? It is pretty weird mystery that there have been no recorded attacks on humans.