Is it because it's a pack in-game?

I'm no wiki/user review expert, but my best guess is that to be user reviewed a game on the wiki must have one or more "releases" listed, and the date for that release must have already taken place, and currently no one has added any releases for Astro's Playroom.

I seem to recall this is the case. When you attempt to create a user review, there's a drop down meu in which you select the platform the game you played was on, and even for console exclusives we need at least one release for that drop down menu to appear.

I could be wrong though, but give it a try.