Because they are Awesome.
Had I known you could request them, I would have requested them.
They are just slow motion features of your character firing his bow/spell...
I get why melee kill cams are requested (since I like them as well, even if they get repetitive after a while), but you don't have any variety whatsoever in ranged kill moves, which is why I think they left them out in the first place.
If they weren't bugged I wouldn't mind them as much, but as they are now, they are completely useless.