I agree. Orcas are known to have multi-generational culture to at least a limited extent; perhaps orcas remember commercial whaling and know humans are skilled at killing whales when we choose to. Or maybe they could work that out just by observing what we can do today.

I doubt attacking humans would be good for orcas in the long run, and perhaps their intellect allows them to generally understand this while sharks don't. (Orcas don't even nibble on humans out of curiosity, so how would they know we don't taste delicious? In this regard sharks seem more curious than orcas, which is seems strange since they're otherwise very curious animals.)