Pretty sure suicide actually is a crime because if you damage some one else or their property in the act, even though you are no longer physically present to prosecute, those harmed or damaged by your action can seek redress in the courts. IOW if the rifle round you fire through your head goes on to kill a 7 year old in the next house your estate can and will be sued.
Hell, if the fuzz stumble onto you in the middle of you trying to off yourself and you dont comply with them, they can shoot you until you do.