IIUC APNGs compress the delta between frames. So 2 frames in a video have mostly similar pixels, and so will compress very well. And even on still images, PNGs

IIUC APNGs compress the delta between frames. So 2 frames in a video have mostly similar pixels, and so will compress very well. And even on still images, PNGs have much better compression. From the same principle that nearby pixels usually have similar values. Gifs store every frame as a separate image and use very crude compression. Also the very limited color palette as others mentioned.