system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some .gif files take longer to load than a better quality, even longer, video?
gpt
Ok, so first you're going to need to know a bit about compression. Say you had a text file that's full of nothing but the letter A over and over, for like a thousand A's. You could represent that in a lot less space by writing "A x 1000". 

In a GIF file, it's stored sorta the same way. Instead of going "green pixel, green pixel, green pixel, blue pixel", it stores it as "green pixel x 3, blue pixel", saving big patches of the same color as one big block of that color, instead of recording each pixel individually. This works really well for simple, cartoony images, with large sections of the same color, but it doesn't work very well for photographic images with lots of shades to them. GIFs are just plain bad for photographic images, which is what high quality videos are made from.

On top of the fact that GIF is bad at photos, proper video codecs are optimized not only for photographic images, but they can compress images through time. In a GIF file, each frame is a separate picture, compressed individually, and no matter what's on the next frame, it compresses the same, whereas video codecs can compare similar frames, figure out which parts are moving faster than others, and not have to store parts of the background for each frame.