What most people think of as trading cards actually began as cigarette cards. Introduced in the 1870s, they were a way to turn a liability into an asset. Early cigarette packs were very flimsy, so manufacturers used cards to stiffen them.
They then took advantage of advances in printing to turn cigarette cards into collectables, building brand loyalty by issuing card sets. It's the same technique used by teams today. You have to catch them all.