I heard that APNGs used to work, but then people just uploaded their APNGs instead of using emotes, and using emotes from different servers is the main selling

I heard that APNGs used to work, but then people just uploaded their APNGs instead of using emotes, and using emotes from different servers is the main selling point of Dicord's freemium "nitro" AFAIK... Another reason could be that Discord caches images on its servers to hide viewer's IP from the original server hosting the image. The caching involves compression that sometimes breaks the image.