Because in your excitement, you threw the first one in the mail without a stamp. And though you wanted to lie in wait and intercept the post-person the next day, you had an appointment at the very time the mail was supposed to be collected, so you couldn't be there.
So instead you took a giant piece of cardboard, glued a white piece of paper to it, bordered it with purple leopard print duct tape, and wrote a message to the mail carrier: PLEASE HELP! Please find this postcard (drawing included) and put this stamp (stamp included also, taped to the center of the piece of cardboard) on it. Much gratitude! and threw that into the mailbox, too. Maybe he or she would glimpse it, and feel generous!
But JUST IN CASE none of these theatrics worked, you made another card. Something will get there!