The appearance of a science fiction story on AMV is unpredictable. It could be anytime based on factors like the creator's inspiration, available resources, and audience demand. So, you just have to keep an eye out for it.
For a love story AMV to be outstanding, it needs a well-chosen song that conveys the emotions of the story. Also, the editing has to be seamless, with smooth transitions between scenes. The quality and clarity of the video clips matter a lot too.
Maybe it's because the market demand for it is relatively small, or there might be certain social or cultural barriers preventing its widespread production.