The first time we see an older Looper who is not properly killed,
they do that horrific thing where they carve a message into his arm about his needing to go to an address, and then begin surgically removing body parts to get him to obey.
Yet later in the film when
Joe kills himself, we see that his older self ceases to exist upon the death of his younger self.
Why didn't they simply kill the younger Looper in order to eliminate the older Looper?