Here's a bookmarklet that gives you video controls: http://slbkbs.org/jsgif/

It lets you play it backwards, frame by frame and change the speed.

My guess is that nobody wants to get their hands dirty working on what's probably very old code for a very old format.

That and maybe the fact that it's probably not very easy to travel back and forward in GIF's incrementally painted animation model described by Gankro in https://news.ycombinator.com/item?id=12333329

I made a Chrome extension that opens a player on specifically selected gifs but not wholesale (would need too much memory)

https://github.com/0ui/gif-scrubber