system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do GIFs load so slow although I have fast internet?
gpt
I take it you mean animated GIFs? Two possible reasons, one is that the site hosting the GIF serving slowly (you can only download as fast as the other side is sending) and another is that animated DIFs are actually really large, must larger than proper video files would be. They're not very good at compressing photos or compressing motion, so when you put those both together (eg. film clips) then GIF is pretty much the worst format for it.

The reason it's popular is because it's still much easier to host GIFs than it is to host videos, and browsers play back looping GIFs better than looping video files.