The idea is to offer all our users the best possible selection of games, DLCs, in-game items, playtime and more. Ideally all the games and game related items you could desire.
GFS is still small and as such it is difficult for us to obtain all games and items at favorable prices. (More on this: Where do you get the game keys from?)
Since we can't add everything at once, we prioritise by user demand through our Game Wishlist.
The more requests we receive for a game or item the sooner we try to integrate it into the shop.