If this movie (and admittedly countless others) has taught me anything, it's that when fighting someone who wants to kill you, don't stop hitting them until you see brain leaking from their head.
Don't love tap them then turn your back on them.
That's an interesting point. I recall how it really struck home after Wolf Creek in particular.
But it's also a true thing: most people aren't killers. I recall a study done after world war ii demonstrating that a significant number of ground forces in combat never fired their weapons directly at the enemy, even when under fire themselves.
Of course movies can't just depict real life. There are dramatic conventions that have to be followed if the story is to satisfy & one is that characters' learning evolves, not necessarily in correlation with society's. So I imagine as the genre develops more characters will take mores steps to ensure their antagonists are really disabled before moving on with the story.
That being said, the filmmakers might have done so here because they had multiple antagonists to work with.