Maybe it is an instinct, an instinct in the same way we humans tend to not eat rotten meat or maggots in wounds. But humans have not been around for so long so I am not sure how deep such an instinct might be. Maybe it is a preference for "seafood".
Or they understand that we are dangerous to have as enemies. Either through recent observation or through some type of communication that has been passed down through the generations. It is not that long ago since we stoped killing killer whales; less than a hundred years, some of them might have been alive and still remember.
There are records of untrained killer whales hunting together with humans; so some of them certainly understand what we are capable of.
https://en.wikipedia.org/wiki/Old_Tom_(orca)
Or they understand that we are dangerous to have as enemies. Either through recent observation or through some type of communication that has been passed down through the generations. It is not that long ago since we stoped killing killer whales; less than a hundred years, some of them might have been alive and still remember.
There are records of untrained killer whales hunting together with humans; so some of them certainly understand what we are capable of. https://en.wikipedia.org/wiki/Old_Tom_(orca)