One thing they're not great for though is shareability. With gifs, you can generally just drag & drop them between most apps and they'll behave as you expect. Not true with videos.
Gifs have limitations and limitations benefit art.
The site doesn't seem to work with GIF's limitations for artistic purposes. It's just slow.
BTW: https://gif.ski can work around most of the visual limitations of GIF, so only poor compression remains.
You can configure HTML video to (by default) show no controls and auto-loop so they’ll be indistinguishable from gifs on a first look, but better in every other way.