It's about how easy it is. In some parts of Africa you do get Lions that prey on humans.
If Lions who attack humans always get killed, only the ones that don't survives and reproduces.
If Lions who attack humans always get killed, only the ones that don't survives and reproduces.
If it's about opportunity (makes sense, catching a human does seem easier than an antelope) rather than anything intrinsic to human flesh, then why would killing them so that they don't reproduce matter? "Opportunity" does not get transmitted genetically.