That likely has to do with the content of the gif. There exists tons of sex gifs, so unless it's particularly impressive in some fashion most people (with rating power) won't care for it.
The file size doesn't likely help for the amount of content that is actually in the image imo, though perhaps not very avoidable given how the camera is slowly panning preventing reusable frames. I'm not sure how the originally looked, but her movements also seem somewhat jerky.
