Apparently cats have to be taught to kill by their mother. Maybe this leopard was bred and reared in a zoo and never learned to hunt and kill prey.
That’s my guess.
I once watched a farm cat teach her 2 or 3 month old kittens to kill mice. She caught a live mouse, and gently held it in her mouth, then dropped it in the middle of a 1 acre mown lawn for the kittens to “play” with. When they were distracted adn the terrified mouse would sprint for the bushes 100’ away, she’d bring it back and start again. Finally the mother cat carefully gnawed off one rear leg of the mouse to slow it down. After a while the kittens began to get the idea, and started chasing and pouncing on the doomed mouse, which was a living teaching aide.