well my science teacher would buy cards during class on ebay. i guess it could be a social matter, like the more cards the hgher you are. or just for fun see how many you can have.
or its just for fun...i still have all of mine which is a shit load...people collect a certain player or they get everyone from a team that year or some people like to get the complete set of the certain type of cards...i think its fun to go back and look at em...i'm still big in to autographs i probably got 200+ but thats including baseballs and bats too