When did You Stop Caring?
At what point did you realize, you no longer cared about the 40k fluff??
This is more for the senior members, but I find that there is going to be a point in every fans life cycle where they just don't care about the fluff. We all still like 40k, but we no longer obsess about knowing every detail, or who could beat who, or even posting on a forum is too much work.
It's the nature of this fandom. There is nothing changing story wise, and even this forum, has the same posts today as it did when I signed up in 2010, just new authors.
So again when did you stop caring? Mine easily was after Know No Fear and First Heretic. I enjoyed the books and wanted to know more, but I stopped going to this forum heavily after those books. I found I didn't really care what others thought on this universe.