Couple of reasons I can think of.
First, we don't know that Satan wanted to kill Jesus. He might just have wanted to 'break' him. To have him deny God, or curse God, or deny the people He was sent to save; or to get him to hate those people instead of love and show mercy. That is more up his alley, isn't it? Having one of his closest brothers betray him would be a good way to accomplish that. Having his own people (Israel) deny Him is another, listening instead to lies over the truth.
Second, how do we know that Satan even knew all that God would bring about? Even Christ did not know everything about what God planned to do.
Peace,
tammy