He stepped on the trap!
|Black bear steps on a trap|
And walked away. The problem is that he stepped ON it and not in it. The bears have sprung the trap a couple of times and walked off. There are so many variables that come into play to make sure that the trap springs exactly where it needs to and successfully goes up the leg and catches instead of releasing, going off too early or late or having the bears not even go near it.
I have said it before... bear hunting is NOT easy!