The story
Genericized trademark from Diaper Deck, the brand name for a wall-mounted changing table created by the American Infant Care Products Corporation. This product name was first used on 24 April 1986, and is from diaper + deck (“any raised flat surface that can be walked on”) because the baby can walk and lay on the surface of the raised changing table.
Etymology from Wiktionary, CC BY-SA 4.0.