There are certainly reasons to glue the nut in place. The benefit of having it securely in place and easily removable (as a couple dots of white or CA glue) in most cases (in my mind) is worth the extra minute cleaning a spot of glue when the nut needs to be removed. I suppose if one switches between gut and steel strings often on the same bass and had a nut for each, then you wouldn't want it glued. But it's mostly standard practice (if such a thing exists in the bass world) to glue them.
