There is no point of adding a category with no runs to the leaderboard. Furthermore, following the definition of All Missions, this list is incomplete. A more accurate name would be All Story Missions.

There has been multiple discussions about this category in the past, I suggest you look around and read them.

I like how he just commands us to add it, rather than asking nicely

Hey guys, you better add a category that NOBODY will EVER run and that has no existing runs anyway to the leaderboard, or I'll be angry!!!