2.5D Sprite always face at camera - Unity Answers

This is because when you move an object on the x/y planes and have it look at the camera, the object rotates as if it is moving in to a sphere. Think of it as if it's orbiting around a point. Since you're using the negative camera position, that point is behind the object. This has the virtue of flipping your sprite to the way it should face, but at the detriment of making it rotate as the x and y