Why do monsters leave bodies?

I was reading stuff and I realized like, why do these monsters leave bodies ?? I'm assuming they hunt for survival and food, so then why do they leave bodies instead of taking them/eating them?

I understand if only the bones are left but like they leave whole bodies with just a few scratches and blood for whatever reason,, I don't see missing body parts or like obvious signs of being eaten,, 

Like, are they just killing for the sake of killing?

Thanks for reading my yap session !!