cool question :) i'll take a crack at it.

while patience may have gone down, i don't think it's a significant factor. videos go extremely viral on Facebook and Buzzfeed alongside other forms of content.

in some cases, videos tend to be something that we consume on our own time and it requires a greater context-switch. maybe you want to go on youtube and check our your latest subscriptions' videos. i would guess there is a time and place for people to do that. in the case of reddit, this means it may also be specific to a subreddit's culture. i'd wager a relevant video in a forum full of enthusiasts is going to be received differently than a video on a main subreddit where people are out to consume quick laughs and post witty comments in an attempt to gain karma. in the former case, it's sort of like youtube. "this video looks interesting, i'll definitely watch it later when i get the chance." in /r/funny, one is consuming mindless content and posting mindless comments. very different use-cases and communities.

here's one enormous difference between Facebook/Instagram/Vine vs reddit. in the former instances, the video already starts playing as soon as it's in view, so it catches your attention right away, and if it looks interesting, you'll click it so you can hear it with sound. without that feature, videos are handicapped on reddit.

also, GIFs and funny pictures are a unique phenomenon themselves. they've developed their own subculture and usage today. they make great material for conversation where GIFs/pics can be quickly shared (vs "thanks i'll watch that later if i have time" aka "i don't feel like watching this.") and they can be used to express emotions. pictures can be edited, can be captioned in typical "this is A..." and then punchline "this is B" pattern or whatever patterns are trending at the moment, photos easily edited and combined alongside others to generate new content, etc.

lastly, unlike Facebook, reddit's algorithm is based more strictly on upvotes, whereas Facebook has a separate algorithm that determines what gets put on your feed due to a bunch of factors. in a sheer numbers game where picture content outnumbers videos 100000 to 1 (just pulled that number out of my ass but you get the drift, again, see how easy it is to quickly create new content out of a picture), then pictures are automatically going to dominate a reddit's frontpage.