We can't allow large sized animations for avatars. Avatars are meant to be small, lightweight items. If all (or even some) avatars were of large size it penalizes dial-up or slow broadband users tremendously. As GIF animation must be processed in the browser the larger the animation the greater the performance penalty for the CPU. I suggest, if you are able, to try cutting out duplicate or unnecessary frames in the GIF. It will make it a bit more choppy but may let you reduce the size. Lowering the number of colors (from 256 to 128, for instance) is also worth a shot.