Fast forward 20-30 years and scarcity happened for cards like Mickey Mantle and other hall of fame players and prices shot up to thousands for a single card in mint condition. Kids like me hear that and buy tons of baseball cards. The lore of people with rare cards was talked about at card shops. It was cool to buy a pack and see what you got and trade with friends. Being a baseball fan at the time, it was fun to collect every player on your favorite team, maybe get cards signed by them at a game.
The fun is in the collecting, sharing, memories, etc. I'm sure there are similar stories for things like comic books and other collectibles (first edition books) where earlier releases of things are now rare. If everything were just a flat fee per card nobody would bother.
Buying singles is generally regarded as the best way to build a collection, but it's not as fun as buying a pack or box of cards and seeing what you get. Collecting vs. gambling.
Now they open boxes as a way of talking about baseball and bonding. Valuable cards are just a positive side effect.
But that would not allow you to sell all the bulk(multiple copies of same minimally useful cards) to pad profit margin. Or make the whole thing to lottery (see 1/1 One Ring). Thus driving gamblers to acquire as much product they can.