When uploading photo as the cover image, the photo fills the input box to let the uploader know how it will be shown to the users. One can even zoom in or out to crop it to make it fit better.
However, when uploading GIF as cover, the GIF doesn’t fill the input box. There isn’t a way to know how it is shown to the users. This is particularly an issue for using GIF as the app cover. One cannot know if the GIF will show at the 3:4 aspect ratio.
If zooming and cropping GIF are challenging, it’s ok to not offer these features. But at least the GIF should fill the input box to shown how it will be presented to the users.