Because Apple thinks no one uses GIFs, just like they say no one uses Flash and that no one uses FireWire 400. Gifs still appear here and there, and they're honestly the simplest way of displaying a small, simple animation like a "loading" spinning icon or something. Safari is already horribly bad at playing GIFs and Preview and Quick Look just don't even try to play them. If you ask me, it's sad that something as simple as a GIF plays worse today than 10 years ago! Yes there are less GIFs but GIFs are not gone. Many people have stupid GIFs in their forum signatures and sometimes you just find it funny and want to copy it to your computer and keep it. At a time like that you don't really care about video codecs and modern formats. You just want the animation. While Windows has absolutely no problem playing a GIF whatsoever, on a Mac, you just can't do it properly. Safari takes like 10 minutes and 3 reloads to play a freaking GIF! You can't just pretend they don't exist, they're still part of the web!