That may make the task more difficult, but still, even when I search gifs from very well know series like the Simpsons and I get a bunch of random Simpsons gifs (therefore I assume they got rights for short Simpsons clips) but none is remotely similar to the one I'm looking for. Then I go to google images and there it is among the first results.

Edit: It may have improved a bit lately, but it would be much, much better if they did OCR of text in gifs, and use the context of where the gifs are found (esp. page title) for additional search terms.

If you want Simpsons GIFs, have you checked out Frinkiac?

Yes, currently I know it and use it. It was just an example on top of my head. Other series don't have an equivalent. And of course there's a lot of known gifs that don't come straight from TV. RightGif mentioned in another comment seems to work better for that purpose.

Many of the gifs they show are not owned by the uploader. They acquire the rights in a limited fashion to a small portion of the gifs they show.

They'll of course make the "user generated content" argument, but clipping a video is not user generated content.

How does that actually work? GIFs are often made by random anonymous people and then they just spread. Seems like a big task.