But a bunch of players could get together and decide to play the game however they want, right? If people are upset there are no "rare" cards to play, whey not create a league where certain proxy cards are legal?
Having asked this of a few friends who are MTG league judges: a lot of players feel a sort of "fiscal sympathy" for Wizards. They like the game, and want its continuing development to be incentivized, so they want to pay for cards rather than "pirating" them. Or rather, they want to act in such a way that cards still have value. It's similar to Bitcoin, in a way—nobody who holds the stuff is going around suggesting people should build their own private virtual economies instead.