One thing I have just read is that there might be licensing issues still with GIF. That used to be a headache in the early days of web design, some more affordable image editing tools would not let you compose animated GIFs or even static one-frame GIFs because the rights to the format were owned by CompuServe (I think). Something about the licensing rights still appears to make open-source development surrounding the GIF format difficult.
See here:
https://www.gnu.org/philosophy/gif.en.html
Also, I've just read that APNG appears to be an alternative, and open standard of creating animated images, developed by Mozilla. There is a whole page on it on the Mozilla wiki page: