@sarajw that's certainly true, but if I upload a file I think it's worth ensuring that the format remains the same, because if I want to download it and repost it elsewhere, I get a video, and other applications typically treat videos differently by not looping them, whereas animated GIFs are looped. Thus, there's two possible solutions in my view:
Only display videos (since you're absolutely right that GIFs aren't exactly the most lean format), but allow users to download the original GIFs with the usual Right Click -> Save Image As (not sure how difficult this would be to implement)
Just use the same file format that the original uploaded file is, even if the site will still compress it.
There may be some other solutions out there as well, but I'm not sure exactly what those would be.