One-time pads are obviously not a serious widespread cryptography proposal.
But the question of, "Why not just send the message instead of the pad" is pretty straightforward: when you have the opportunity to safely deliver the pad, you don't know what the message will be. When you do know what the message will be, you don't have the opportunity to safely deliver the pad.
But the question of, "Why not just send the message instead of the pad" is pretty straightforward: when you have the opportunity to safely deliver the pad, you don't know what the message will be. When you do know what the message will be, you don't have the opportunity to safely deliver the pad.