I think if this were really true, gifs wouldn’t exist.
They fill a niche, they’re far more unobtrusively browsable than videos, but are also more dynamic/engaging etc than a still photo for obvious reasons. When you’re in some public bathroom you’ll totally browse gifs for 5m, but I would never click a video link and risk blaring the first 10 seconds until I figured out how to mute the fucking thing. So in a variety of similar contexts, A gif’s silence is a virtue.
So then you think about reddit and what kind of context this site is for a gif. Well... people use reddit in all sorts of different ways, but mobile viewing of text threads is a definitely a huge part of it. So say you’re wanting to react to a comment, in thread, with a video: do you want it to have sound? No. Most people who are reading some text don’t then want to be blindsided with sound at whatever volume their phone happens to be at. Then I’d say you also optimize for load time, since the quick loading will make the gifs integration into the context of a comment thread more seamless.
If you read reddit almost like sitting down for a movie after dinner, sure video is always better, but if you look at it here and there to kill time waiting in line etc, gifs are the perfect format.