87 MB isn't that bad, it's only like, what, about 10 minutes of medium-bitrate footage at 1080p (encoded h264)? lol In all seriousness, though, there is something to be said for the portability of GIF format, though. You can't typically send MP4s as stickers in messaging apps, but you could send this, and it will:
a) loop correctly in basically any environment (I find that many mp4s uploaded here should really be GIFs because they are short, and designed to loop, but most apps don't loop video by default, resulting in a broken experience unless I send someone the link to the video actually on danbooru; this makes viewing the loop a two-click experience that potentially involves going to a moblie browser, which is a worse experience for the end user than just getting an 87mb GIF)
b) Work everywhere, unlike WEBM which, in addition to the problems with two-click viewing described above, has poor adoption and simply doesn't work in some software
So yeah, GIF has terrible compression, but it fills a need that MP4 and WEBM don't fill yet-- portable animated looping image. The problem with WEBM and MP4 is that they are video formats designed for videos, which leaves them with features that a looping animated image doesn't need (sound containers for example), and missing features that a looping animated image wants (looping by default, 0-click playback in most software, compatibility with messaging software for use as stickers).
A better, modern alternative to GIF would be APNG, which is explicitly designed for the kind of looping animated images that GIF carries, but APNG adoption is truly terrible. It's a real struggle to find software that supports it. Ultimately as internet got fast and storage got cheap I think most people just accepted that the inefficiencies of GIF were acceptable. Unfortunate, maybe, but it is what it is.
