I mean in paper magic, you get new cards by buying new cards. You don't get rewards for winning. The arena game is freemium, meaning you can play for free and collect cards, but you're intended to spend money to get the cards you need in a timely manner. Further, they've given us an option to actually pick the exact cards we want as we earn wildcards, while in paper, we're forced to spend crazy amounts on a single card from hobby lobby or something. WotC is a business trying to make a profit, they do this by (you guessed it) getting you to spend money on cards, not by giving them to you for free. If they just give you everything you want or need, they aren't making a profit and the business ceases to exist.

I get it. You want cards, cards and more cards. Must have those uber mythics to build your decks and stomp your opponents.

The fact is the wildcard system is a step WotC has never taken on any other version of the game. They're giving us a metric shit ton by letting us have it. No other version of the game has ever been so liberal. Let's not complain too much that they're not giving us more free stuff.