I don't quite follow. This is because the gif is decoded and played. No different than a video. You don't need a proprietary player to loop a video, you just go back to the start of the video. For streaming, this is only problematic for large videos that can't be cached, but the same applies to large gifs. Browsers can loop video, it's just a right-click setting. HTML5 can loop video, allowing sites to serve video in e.g. a banner, replacing gifs. You can save any video file just like a gif.
> Something that browsers treat as a moving image and not a video.
The entire point of deprecating gifs is because video is superior. Gif as an image format being able to specify frame duration and looping is hardly a noteworthy feature.