Similar to Pokemon, you at least got something tangible. Even if MtG or Pokemon shutdown tomorrow, you can still play with your cards until you die, and then your kids can play with them.
Or you can sell them to other kids or collectors.
> Then you have Mac Donald and their monopoly game.
Also, here you got a tangible benefit (you got fed).
This is the key difference versus paying for Ninja Wars, or even for non-pay2win-stuff like "skins". The second the game servers get shut down is also the second your collection becomes worthless. And if you're done with the game you can't even sell on your stuff to someone else.