It's probably more of a perception thing than anything else. An animated GIF feels like a lot less overhead than a full on video, even if the file itself is smaller as a video.
Also user forums like reddit are a lot more likely to permit images in posts than a video tag, so you get the added portability of being able to post it almost everywhere.
Also user forums like reddit are a lot more likely to permit images in posts than a video tag, so you get the added portability of being able to post it almost everywhere.