Probably for the humans writing, sorting, and manipulating the cards. A big fat stack of cards isn't like a floppy disk, it requires active care and feeding, and you'd better not drop it

Pro tip for time travelers to the 60’s: take a marker pen and draw a diagonal line across the top of your card deck, from column 1 on the first card to column 80 on the last one. It’ll help you sort things out later when you drop it.