Why do players think it's acceptable to have an "economy" for trading virtual gamepieces? Why don't they walk away and play game/culture that charges a flat fee or a time/usage-based subscription?
I simply won't spend on Magic Online since I can't exit. In addition, why should I spend hundreds of dollars on something whose value can plunge drastically?
If you have actual physical cards, you can sell them. Powerful modern cards hold their value reasonably well.
(There's not much guarantee about what sort of economy you'll get... it's easy to get one that pathological in some sense, either psychological or mathematical. But you'll get something.)
They had that entire previously-untapped goldmine of a market space to themselves (or near enough, given the quality of their early competition) for long enough to get really culturally entrenched, and that meant they were able to shift the model online (and keep a much greater chunk of the profits) without as much resistance as you might expect--if you already believe that 5 cents' worth of ink and cardboard can be worth dozens or hundreds of dollars if it's got the right picture on it, it's a lot easier to believe that the same picture on your computer screen can be worth the same.
Money isn't really an object at any kind of serious tournament - everyone has/ can borrow all the cards they need to play.
Those who don't want to pay, have always been able to play for free with GccG and others.