Fred Bear shot a recurve. The arrow was very close to his hand. Recurve shooters can get away with it because the arrow is on the axis of rotation as you cant your bow. With a modern compound, the arrow is a couple of inches above the hand. When you cant a compound, the arrow is moved a much greater distance off the target line. This is why you miss more when canting a compound than with a recurve.

Shoot a couple of groups with your bow tilted in varying degrees and see what happens. You'll see why the level is there...