Also interesting that out of the four DLCs (not counting the Extended Cut), only one actually had you dealing with the Reapers at all!
Four DLCs? I don't think "From Ashes" counts, since it came in the box.
Anyways, from the player's POV, the Reapers had already been done & dusted when they got to the post-release DLC. Telling unrelated stories was the smarter approach there - give players a new reason to return, instead of offering them more of the same.