If you come back anonymous person I'm not quite sure what you asking. Why do I always write Remus rimming Sirius or just an in general sort of question?

For me personally I don't think I ever have one over the other. It's just what ever fits the mood of the character in the story. If it's a general sort of thing I would think most fanfic writers just want to be the one to do that to Sirius so they have Remus do it for them ;-p.