I don't mean "copyright" as in, Wizards would literally sue you for writing "Black Lotus" on a card.
I mean "copyright" as in the act of paying for the game you are playing, rather than reproducing it yourself.
For another example, what stops you from playing Monopoly by just writing "Boardwalk" and "Park Place" on a piece of paper, and drawing up your own fake money and cards? Nothing really, but generally it's considered a good idea to pay for games people make, as a way to reward them for making the game.
I mean "copyright" as in the act of paying for the game you are playing, rather than reproducing it yourself.
For another example, what stops you from playing Monopoly by just writing "Boardwalk" and "Park Place" on a piece of paper, and drawing up your own fake money and cards? Nothing really, but generally it's considered a good idea to pay for games people make, as a way to reward them for making the game.