The banner was reduced from a larger size, but the expression on the egg's face is still visible. The features were left the same. Only the dimensions of the body were reduced. Unnecessary movement means unnecessary file size. Pixels have to be redrawn if they move from frame to frame.
Movement can be too distracting on a textual page.
But animation does allow several frames to be shown in one space. Click here . Lateral Thinking . Faux 3D Gif compression . Gif and jpegs .