This is because your photo is too small. Your photo must be at least 4000 pixels long on one side to be available as Super Large. If possible, please adjust your camera or scanner to output a higher resolution image.
Bigger is not always better, so don't up-res your photos. If you do, the quality will suck and anyone who downloads your photo will feel dirty and cheated. Oh no, the dirt's not coming off! Agh!