Everybody loves a good deal.
Being brought up in the age of capitalism means that we've been conditioned to place a lot of value in what we buy, how expensive it is, and how purchasing these things makes us simultaneously unique and just like everyone else.
You want to buy things that other people have, but you also want to get it for a better price because then you've somehow won the capitalist game.
I'm just as guilty as anyone in this—if something is free, I will take it no matter what it is.