Why cant we boomerangs pre-recorded videos?

I am someone who, if I edit something, would still like documentation of the original. The same goes for videos. If I record something that would be an epic boomerang, thats probably because the moment was epic (and likely cannot be repeated easily). I have not really used boomerang because I would rather just record the original. If there was a way to boomerang portions of pre-recorded videos, then boomerang would be worthwhile for me to use.

the fenix about Boomerang from Instagram, v1.4.2