Because it’s old and easy to handle. Yes it’s wasteful if you convert whole videos, but really anything under 10s with low rez is easily handleable by pretty much anything. Gif was the first animated format and that’s why it’s big. Also early internet forum days were absolutely plastered with pixelart gifs that ran for minutes and barely swalloed 100kb. You can get a lot of bang for your buck if you save on pixels and framerate. But ofc a 60fps render of some 4k bluray clip will eat your memory. Contrast that with 16×32 px gif that runs at 8fps.