Maybe they did it so you'd have something to do other than complain on the internet?
But seriously, you get the rewards after 12 levels that take less than a minute a piece. Then the game actually becomes more fun/challenging. So preodering gets you something to kill some time and introduce the new setting. A lot better than just day 1 items or crappy DLC.
If it's that much of a bother, instead of complaining you could always look up the solutions on IGN. The unlocks you get for the puzzles are gonna be completely worth it. Besides, it's not a bad puzzle game.