Music CDs and vinyl records, console games, etc. You can make perfect copies of each, yet it's not hard to find certain ones that sell for big money (due to rarity, desirability, nostalgia, etc). Some people care about having the "real deal" and will pay for it. It's as simple as that.
I think most people collect PCBs because they have cabs, and for most games there's no really accurate substitute for the original PCB when playing on a cab.